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Add an optimization that does CSE in a group of similar GEPs.
This optimization merges the common part of a group of GEPs, so we can compute each pointer address by adding a simple offset to the common part. The optimization is currently only enabled for the NVPTX backend, where it has a large payoff on some benchmarks. Review: http://reviews.llvm.org/D3462 Patch by Jingyue Wu. llvm-svn: 207783
This commit is contained in:
Eli Bendersky
parent
daef7e1f4b
commit
0602e236ae
@ -238,6 +238,7 @@ void initializeSimpleInlinerPass(PassRegistry&);
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void initializeRegisterCoalescerPass(PassRegistry&);
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void initializeSingleLoopExtractorPass(PassRegistry&);
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void initializeSinkingPass(PassRegistry&);
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void initializeSeparateConstOffsetFromGEPPass(PassRegistry &);
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void initializeSlotIndexesPass(PassRegistry&);
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void initializeSpillPlacementPass(PassRegistry&);
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void initializeStackProtectorPass(PassRegistry&);
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@ -156,6 +156,7 @@ namespace {
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(void) llvm::createBBVectorizePass();
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(void) llvm::createPartiallyInlineLibCallsPass();
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(void) llvm::createScalarizerPass();
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(void) llvm::createSeparateConstOffsetFromGEPPass();
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(void)new llvm::IntervalPartition();
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(void)new llvm::FindUsedTypes();
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@ -377,6 +377,12 @@ FunctionPass *createScalarizerPass();
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// AddDiscriminators - Add DWARF path discriminators to the IR.
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FunctionPass *createAddDiscriminatorsPass();
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//===----------------------------------------------------------------------===//
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//
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// SeparateConstOffsetFromGEP - Split GEPs for better CSE
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//
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FunctionPass *createSeparateConstOffsetFromGEPPass();
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} // End llvm namespace
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#endif
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@ -147,10 +147,23 @@ void NVPTXPassConfig::addIRPasses() {
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addPass(createNVPTXAssignValidGlobalNamesPass());
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addPass(createGenericToNVVMPass());
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addPass(createNVPTXFavorNonGenericAddrSpacesPass());
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// The FavorNonGenericAddrSpaces pass may remove instructions and leave some
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// values unused. Therefore, we run a DCE pass right afterwards. We could
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// remove unused values in an ad-hoc manner, but it requires manual work and
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// might be error-prone.
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addPass(createSeparateConstOffsetFromGEPPass());
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// The SeparateConstOffsetFromGEP pass creates variadic bases that can be used
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// by multiple GEPs. Run GVN or EarlyCSE to really reuse them. GVN generates
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// significantly better code than EarlyCSE for some of our benchmarks.
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if (getOptLevel() == CodeGenOpt::Aggressive)
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addPass(createGVNPass());
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else
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addPass(createEarlyCSEPass());
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// Both FavorNonGenericAddrSpaces and SeparateConstOffsetFromGEP may leave
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// some dead code. We could remove dead code in an ad-hoc manner, but that
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// requires manual work and might be error-prone.
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//
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// The FavorNonGenericAddrSpaces pass shortcuts unnecessary addrspacecasts,
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// and leave them unused.
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//
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// SeparateConstOffsetFromGEP rebuilds a new index from the old index, and the
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// old index and some of its intermediate results may become unused.
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addPass(createDeadCodeEliminationPass());
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}
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@ -64,6 +64,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
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initializeStructurizeCFGPass(Registry);
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initializeSinkingPass(Registry);
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initializeTailCallElimPass(Registry);
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initializeSeparateConstOffsetFromGEPPass(Registry);
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}
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void LLVMInitializeScalarOpts(LLVMPassRegistryRef R) {
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583
lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
Normal file
583
lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
Normal file
@ -0,0 +1,583 @@
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//===-- SeparateConstOffsetFromGEP.cpp - ------------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Loop unrolling may create many similar GEPs for array accesses.
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// e.g., a 2-level loop
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//
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// float a[32][32]; // global variable
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//
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// for (int i = 0; i < 2; ++i) {
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// for (int j = 0; j < 2; ++j) {
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// ...
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// ... = a[x + i][y + j];
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// ...
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// }
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// }
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//
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// will probably be unrolled to:
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//
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// gep %a, 0, %x, %y; load
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// gep %a, 0, %x, %y + 1; load
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// gep %a, 0, %x + 1, %y; load
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// gep %a, 0, %x + 1, %y + 1; load
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//
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// LLVM's GVN does not use partial redundancy elimination yet, and is thus
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// unable to reuse (gep %a, 0, %x, %y). As a result, this misoptimization incurs
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// significant slowdown in targets with limited addressing modes. For instance,
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// because the PTX target does not support the reg+reg addressing mode, the
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// NVPTX backend emits PTX code that literally computes the pointer address of
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// each GEP, wasting tons of registers. It emits the following PTX for the
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// first load and similar PTX for other loads.
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//
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// mov.u32 %r1, %x;
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// mov.u32 %r2, %y;
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// mul.wide.u32 %rl2, %r1, 128;
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// mov.u64 %rl3, a;
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// add.s64 %rl4, %rl3, %rl2;
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// mul.wide.u32 %rl5, %r2, 4;
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// add.s64 %rl6, %rl4, %rl5;
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// ld.global.f32 %f1, [%rl6];
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//
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// To reduce the register pressure, the optimization implemented in this file
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// merges the common part of a group of GEPs, so we can compute each pointer
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// address by adding a simple offset to the common part, saving many registers.
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//
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// It works by splitting each GEP into a variadic base and a constant offset.
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// The variadic base can be computed once and reused by multiple GEPs, and the
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// constant offsets can be nicely folded into the reg+immediate addressing mode
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// (supported by most targets) without using any extra register.
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//
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// For instance, we transform the four GEPs and four loads in the above example
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// into:
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//
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// base = gep a, 0, x, y
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// load base
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// laod base + 1 * sizeof(float)
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// load base + 32 * sizeof(float)
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// load base + 33 * sizeof(float)
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//
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// Given the transformed IR, a backend that supports the reg+immediate
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// addressing mode can easily fold the pointer arithmetics into the loads. For
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// example, the NVPTX backend can easily fold the pointer arithmetics into the
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// ld.global.f32 instructions, and the resultant PTX uses much fewer registers.
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//
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// mov.u32 %r1, %tid.x;
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// mov.u32 %r2, %tid.y;
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// mul.wide.u32 %rl2, %r1, 128;
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// mov.u64 %rl3, a;
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// add.s64 %rl4, %rl3, %rl2;
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// mul.wide.u32 %rl5, %r2, 4;
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// add.s64 %rl6, %rl4, %rl5;
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// ld.global.f32 %f1, [%rl6]; // so far the same as unoptimized PTX
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// ld.global.f32 %f2, [%rl6+4]; // much better
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// ld.global.f32 %f3, [%rl6+128]; // much better
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// ld.global.f32 %f4, [%rl6+132]; // much better
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Scalar.h"
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using namespace llvm;
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static cl::opt<bool> DisableSeparateConstOffsetFromGEP(
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"disable-separate-const-offset-from-gep", cl::init(false),
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cl::desc("Do not separate the constant offset from a GEP instruction"),
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cl::Hidden);
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namespace {
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/// \brief A helper class for separating a constant offset from a GEP index.
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///
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/// In real programs, a GEP index may be more complicated than a simple addition
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/// of something and a constant integer which can be trivially splitted. For
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/// example, to split ((a << 3) | 5) + b, we need to search deeper for the
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/// constant offset, so that we can seperate the index to (a << 3) + b and 5.
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///
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/// Therefore, this class looks into the expression that computes a given GEP
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/// index, and tries to find a constant integer that can be hoisted to the
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/// outermost level of the expression as an addition. Not every constant in an
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/// expression can jump out. e.g., we cannot transform (b * (a + 5)) to (b * a +
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/// 5); nor can we transform (3 * (a + 5)) to (3 * a + 5), however in this case,
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/// -instcombine probably already optimized (3 * (a + 5)) to (3 * a + 15).
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class ConstantOffsetExtractor {
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public:
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/// Extracts a constant offset from the given GEP index. It outputs the
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/// numeric value of the extracted constant offset (0 if failed), and a
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/// new index representing the remainder (equal to the original index minus
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/// the constant offset).
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/// \p Idx The given GEP index
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/// \p NewIdx The new index to replace
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/// \p DL The datalayout of the module
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/// \p IP Calculating the new index requires new instructions. IP indicates
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/// where to insert them (typically right before the GEP).
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static int64_t Extract(Value *Idx, Value *&NewIdx, const DataLayout *DL,
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Instruction *IP);
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/// Looks for a constant offset without extracting it. The meaning of the
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/// arguments and the return value are the same as Extract.
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static int64_t Find(Value *Idx, const DataLayout *DL);
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private:
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ConstantOffsetExtractor(const DataLayout *Layout, Instruction *InsertionPt)
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: DL(Layout), IP(InsertionPt) {}
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/// Searches the expression that computes V for a constant offset. If the
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/// searching is successful, update UserChain as a path from V to the constant
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/// offset.
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int64_t find(Value *V);
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/// A helper function to look into both operands of a binary operator U.
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/// \p IsSub Whether U is a sub operator. If so, we need to negate the
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/// constant offset at some point.
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int64_t findInEitherOperand(User *U, bool IsSub);
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/// After finding the constant offset and how it is reached from the GEP
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/// index, we build a new index which is a clone of the old one except the
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/// constant offset is removed. For example, given (a + (b + 5)) and knowning
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/// the constant offset is 5, this function returns (a + b).
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///
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/// We cannot simply change the constant to zero because the expression that
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/// computes the index or its intermediate result may be used by others.
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Value *rebuildWithoutConstantOffset();
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// A helper function for rebuildWithoutConstantOffset that rebuilds the direct
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// user (U) of the constant offset (C).
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Value *rebuildLeafWithoutConstantOffset(User *U, Value *C);
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/// Returns a clone of U except the first occurrence of From with To.
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Value *cloneAndReplace(User *U, Value *From, Value *To);
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/// Returns true if LHS and RHS have no bits in common, i.e., LHS | RHS == 0.
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bool NoCommonBits(Value *LHS, Value *RHS) const;
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/// Computes which bits are known to be one or zero.
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/// \p KnownOne Mask of all bits that are known to be one.
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/// \p KnownZero Mask of all bits that are known to be zero.
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void ComputeKnownBits(Value *V, APInt &KnownOne, APInt &KnownZero) const;
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/// Finds the first use of Used in U. Returns -1 if not found.
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static unsigned FindFirstUse(User *U, Value *Used);
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/// The path from the constant offset to the old GEP index. e.g., if the GEP
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/// index is "a * b + (c + 5)". After running function find, UserChain[0] will
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/// be the constant 5, UserChain[1] will be the subexpression "c + 5", and
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/// UserChain[2] will be the entire expression "a * b + (c + 5)".
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///
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/// This path helps rebuildWithoutConstantOffset rebuild the new GEP index.
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SmallVector<User *, 8> UserChain;
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/// The data layout of the module. Used in ComputeKnownBits.
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const DataLayout *DL;
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Instruction *IP; /// Insertion position of cloned instructions.
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};
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/// \brief A pass that tries to split every GEP in the function into a variadic
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/// base and a constant offset. It is a FuntionPass because searching for the
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/// constant offset may inspect other basic blocks.
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class SeparateConstOffsetFromGEP : public FunctionPass {
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public:
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static char ID;
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SeparateConstOffsetFromGEP() : FunctionPass(ID) {
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initializeSeparateConstOffsetFromGEPPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<DataLayoutPass>();
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AU.addRequired<TargetTransformInfo>();
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}
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bool runOnFunction(Function &F) override;
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private:
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/// Tries to split the given GEP into a variadic base and a constant offset,
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/// and returns true if the splitting succeeds.
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bool splitGEP(GetElementPtrInst *GEP);
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/// Finds the constant offset within each index, and accumulates them. This
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/// function only inspects the GEP without changing it. The output
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/// NeedsExtraction indicates whether we can extract a non-zero constant
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/// offset from any index.
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int64_t accumulateByteOffset(GetElementPtrInst *GEP, const DataLayout *DL,
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bool &NeedsExtraction);
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};
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} // anonymous namespace
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char SeparateConstOffsetFromGEP::ID = 0;
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INITIALIZE_PASS_BEGIN(
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SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
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"Split GEPs to a variadic base and a constant offset for better CSE", false,
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false)
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INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
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INITIALIZE_PASS_DEPENDENCY(DataLayoutPass)
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INITIALIZE_PASS_END(
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SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
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"Split GEPs to a variadic base and a constant offset for better CSE", false,
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false)
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FunctionPass *llvm::createSeparateConstOffsetFromGEPPass() {
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return new SeparateConstOffsetFromGEP();
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}
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int64_t ConstantOffsetExtractor::findInEitherOperand(User *U, bool IsSub) {
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assert(U->getNumOperands() == 2);
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int64_t ConstantOffset = find(U->getOperand(0));
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// If we found a constant offset in the left operand, stop and return that.
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// This shortcut might cause us to miss opportunities of combining the
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// constant offsets in both operands, e.g., (a + 4) + (b + 5) => (a + b) + 9.
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// However, such cases are probably already handled by -instcombine,
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// given this pass runs after the standard optimizations.
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if (ConstantOffset != 0) return ConstantOffset;
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ConstantOffset = find(U->getOperand(1));
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// If U is a sub operator, negate the constant offset found in the right
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// operand.
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return IsSub ? -ConstantOffset : ConstantOffset;
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}
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int64_t ConstantOffsetExtractor::find(Value *V) {
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// TODO(jingyue): We can even trace into integer/pointer casts, such as
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// inttoptr, ptrtoint, bitcast, and addrspacecast. We choose to handle only
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// integers because it gives good enough results for our benchmarks.
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assert(V->getType()->isIntegerTy());
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User *U = dyn_cast<User>(V);
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// We cannot do much with Values that are not a User, such as BasicBlock and
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// MDNode.
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if (U == nullptr) return 0;
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int64_t ConstantOffset = 0;
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if (ConstantInt *CI = dyn_cast<ConstantInt>(U)) {
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// Hooray, we found it!
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ConstantOffset = CI->getSExtValue();
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} else if (Operator *O = dyn_cast<Operator>(U)) {
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// The GEP index may be more complicated than a simple addition of a
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// varaible and a constant. Therefore, we trace into subexpressions for more
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// hoisting opportunities.
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switch (O->getOpcode()) {
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case Instruction::Add: {
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ConstantOffset = findInEitherOperand(U, false);
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break;
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}
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case Instruction::Sub: {
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ConstantOffset = findInEitherOperand(U, true);
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break;
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}
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case Instruction::Or: {
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// If LHS and RHS don't have common bits, (LHS | RHS) is equivalent to
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// (LHS + RHS).
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if (NoCommonBits(U->getOperand(0), U->getOperand(1)))
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ConstantOffset = findInEitherOperand(U, false);
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break;
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}
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case Instruction::SExt: {
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// For safety, we trace into sext only when its operand is marked
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// "nsw" because xxx.nsw guarantees no signed wrap. e.g., we can safely
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// transform "sext (add nsw a, 5)" into "add nsw (sext a), 5".
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) {
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if (BO->hasNoSignedWrap())
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ConstantOffset = find(U->getOperand(0));
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}
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break;
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}
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case Instruction::ZExt: {
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// Similarly, we trace into zext only when its operand is marked with
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// "nuw" because zext (add nuw a, b) == add nuw (zext a), (zext b).
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) {
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if (BO->hasNoUnsignedWrap())
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ConstantOffset = find(U->getOperand(0));
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}
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break;
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}
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}
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}
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// If we found a non-zero constant offset, adds it to the path for future
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// transformation (rebuildWithoutConstantOffset). Zero is a valid constant
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// offset, but doesn't help this optimization.
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if (ConstantOffset != 0)
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UserChain.push_back(U);
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return ConstantOffset;
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}
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unsigned ConstantOffsetExtractor::FindFirstUse(User *U, Value *Used) {
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for (unsigned I = 0, E = U->getNumOperands(); I < E; ++I) {
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if (U->getOperand(I) == Used)
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return I;
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}
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return -1;
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}
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Value *ConstantOffsetExtractor::cloneAndReplace(User *U, Value *From,
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Value *To) {
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// Finds in U the first use of From. It is safe to ignore future occurrences
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// of From, because findInEitherOperand similarly stops searching the right
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// operand when the first operand has a non-zero constant offset.
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unsigned OpNo = FindFirstUse(U, From);
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assert(OpNo != (unsigned)-1 && "UserChain wasn't built correctly");
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// ConstantOffsetExtractor::find only follows Operators (i.e., Instructions
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// and ConstantExprs). Therefore, U is either an Instruction or a
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// ConstantExpr.
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if (Instruction *I = dyn_cast<Instruction>(U)) {
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Instruction *Clone = I->clone();
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Clone->setOperand(OpNo, To);
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Clone->insertBefore(IP);
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return Clone;
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}
|
||||
// cast<Constant>(To) is safe because a ConstantExpr only uses Constants.
|
||||
return cast<ConstantExpr>(U)
|
||||
->getWithOperandReplaced(OpNo, cast<Constant>(To));
|
||||
}
|
||||
|
||||
Value *ConstantOffsetExtractor::rebuildLeafWithoutConstantOffset(User *U,
|
||||
Value *C) {
|
||||
assert(U->getNumOperands() <= 2 &&
|
||||
"We didn't trace into any operator with more than 2 operands");
|
||||
// If U has only one operand which is the constant offset, removing the
|
||||
// constant offset leaves U as a null value.
|
||||
if (U->getNumOperands() == 1)
|
||||
return Constant::getNullValue(U->getType());
|
||||
|
||||
// U->getNumOperands() == 2
|
||||
unsigned OpNo = FindFirstUse(U, C); // U->getOperand(OpNo) == C
|
||||
assert(OpNo < 2 && "UserChain wasn't built correctly");
|
||||
Value *TheOther = U->getOperand(1 - OpNo); // The other operand of U
|
||||
// If U = C - X, removing C makes U = -X; otherwise U will simply be X.
|
||||
if (!isa<SubOperator>(U) || OpNo == 1)
|
||||
return TheOther;
|
||||
if (isa<ConstantExpr>(U))
|
||||
return ConstantExpr::getNeg(cast<Constant>(TheOther));
|
||||
return BinaryOperator::CreateNeg(TheOther, "", IP);
|
||||
}
|
||||
|
||||
Value *ConstantOffsetExtractor::rebuildWithoutConstantOffset() {
|
||||
assert(UserChain.size() > 0 && "you at least found a constant, right?");
|
||||
// Start with the constant and go up through UserChain, each time building a
|
||||
// clone of the subexpression but with the constant removed.
|
||||
// e.g., to build a clone of (a + (b + (c + 5)) but with the 5 removed, we
|
||||
// first c, then (b + c), and finally (a + (b + c)).
|
||||
//
|
||||
// Fast path: if the GEP index is a constant, simply returns 0.
|
||||
if (UserChain.size() == 1)
|
||||
return ConstantInt::get(UserChain[0]->getType(), 0);
|
||||
|
||||
Value *Remainder =
|
||||
rebuildLeafWithoutConstantOffset(UserChain[1], UserChain[0]);
|
||||
for (size_t I = 2; I < UserChain.size(); ++I)
|
||||
Remainder = cloneAndReplace(UserChain[I], UserChain[I - 1], Remainder);
|
||||
return Remainder;
|
||||
}
|
||||
|
||||
int64_t ConstantOffsetExtractor::Extract(Value *Idx, Value *&NewIdx,
|
||||
const DataLayout *DL,
|
||||
Instruction *IP) {
|
||||
ConstantOffsetExtractor Extractor(DL, IP);
|
||||
// Find a non-zero constant offset first.
|
||||
int64_t ConstantOffset = Extractor.find(Idx);
|
||||
if (ConstantOffset == 0)
|
||||
return 0;
|
||||
// Then rebuild a new index with the constant removed.
|
||||
NewIdx = Extractor.rebuildWithoutConstantOffset();
|
||||
return ConstantOffset;
|
||||
}
|
||||
|
||||
int64_t ConstantOffsetExtractor::Find(Value *Idx, const DataLayout *DL) {
|
||||
return ConstantOffsetExtractor(DL, nullptr).find(Idx);
|
||||
}
|
||||
|
||||
void ConstantOffsetExtractor::ComputeKnownBits(Value *V, APInt &KnownOne,
|
||||
APInt &KnownZero) const {
|
||||
IntegerType *IT = cast<IntegerType>(V->getType());
|
||||
KnownOne = APInt(IT->getBitWidth(), 0);
|
||||
KnownZero = APInt(IT->getBitWidth(), 0);
|
||||
llvm::ComputeMaskedBits(V, KnownZero, KnownOne, DL, 0);
|
||||
}
|
||||
|
||||
bool ConstantOffsetExtractor::NoCommonBits(Value *LHS, Value *RHS) const {
|
||||
assert(LHS->getType() == RHS->getType() &&
|
||||
"LHS and RHS should have the same type");
|
||||
APInt LHSKnownOne, LHSKnownZero, RHSKnownOne, RHSKnownZero;
|
||||
ComputeKnownBits(LHS, LHSKnownOne, LHSKnownZero);
|
||||
ComputeKnownBits(RHS, RHSKnownOne, RHSKnownZero);
|
||||
return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
|
||||
}
|
||||
|
||||
int64_t SeparateConstOffsetFromGEP::accumulateByteOffset(
|
||||
GetElementPtrInst *GEP, const DataLayout *DL, bool &NeedsExtraction) {
|
||||
NeedsExtraction = false;
|
||||
int64_t AccumulativeByteOffset = 0;
|
||||
gep_type_iterator GTI = gep_type_begin(*GEP);
|
||||
for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
|
||||
if (isa<SequentialType>(*GTI)) {
|
||||
// Tries to extract a constant offset from this GEP index.
|
||||
int64_t ConstantOffset =
|
||||
ConstantOffsetExtractor::Find(GEP->getOperand(I), DL);
|
||||
if (ConstantOffset != 0) {
|
||||
NeedsExtraction = true;
|
||||
// A GEP may have multiple indices. We accumulate the extracted
|
||||
// constant offset to a byte offset, and later offset the remainder of
|
||||
// the original GEP with this byte offset.
|
||||
AccumulativeByteOffset +=
|
||||
ConstantOffset * DL->getTypeAllocSize(GTI.getIndexedType());
|
||||
}
|
||||
}
|
||||
}
|
||||
return AccumulativeByteOffset;
|
||||
}
|
||||
|
||||
bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
|
||||
// Skip vector GEPs.
|
||||
if (GEP->getType()->isVectorTy())
|
||||
return false;
|
||||
|
||||
// The backend can already nicely handle the case where all indices are
|
||||
// constant.
|
||||
if (GEP->hasAllConstantIndices())
|
||||
return false;
|
||||
|
||||
bool Changed = false;
|
||||
|
||||
// Shortcuts integer casts. Eliminating these explicit casts can make
|
||||
// subsequent optimizations more obvious: ConstantOffsetExtractor needn't
|
||||
// trace into these casts.
|
||||
if (GEP->isInBounds()) {
|
||||
// Doing this to inbounds GEPs is safe because their indices are guaranteed
|
||||
// to be non-negative and in bounds.
|
||||
gep_type_iterator GTI = gep_type_begin(*GEP);
|
||||
for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
|
||||
if (isa<SequentialType>(*GTI)) {
|
||||
if (Operator *O = dyn_cast<Operator>(GEP->getOperand(I))) {
|
||||
if (O->getOpcode() == Instruction::SExt ||
|
||||
O->getOpcode() == Instruction::ZExt) {
|
||||
GEP->setOperand(I, O->getOperand(0));
|
||||
Changed = true;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
const DataLayout *DL = &getAnalysis<DataLayoutPass>().getDataLayout();
|
||||
bool NeedsExtraction;
|
||||
int64_t AccumulativeByteOffset =
|
||||
accumulateByteOffset(GEP, DL, NeedsExtraction);
|
||||
|
||||
if (!NeedsExtraction)
|
||||
return Changed;
|
||||
// Before really splitting the GEP, check whether the backend supports the
|
||||
// addressing mode we are about to produce. If no, this splitting probably
|
||||
// won't be beneficial.
|
||||
TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>();
|
||||
if (!TTI.isLegalAddressingMode(GEP->getType()->getElementType(),
|
||||
/*BaseGV=*/nullptr, AccumulativeByteOffset,
|
||||
/*HasBaseReg=*/true, /*Scale=*/0)) {
|
||||
return Changed;
|
||||
}
|
||||
|
||||
// Remove the constant offset in each GEP index. The resultant GEP computes
|
||||
// the variadic base.
|
||||
gep_type_iterator GTI = gep_type_begin(*GEP);
|
||||
for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
|
||||
if (isa<SequentialType>(*GTI)) {
|
||||
Value *NewIdx = nullptr;
|
||||
// Tries to extract a constant offset from this GEP index.
|
||||
int64_t ConstantOffset =
|
||||
ConstantOffsetExtractor::Extract(GEP->getOperand(I), NewIdx, DL, GEP);
|
||||
if (ConstantOffset != 0) {
|
||||
assert(NewIdx && "ConstantOffset != 0 implies NewIdx is set");
|
||||
GEP->setOperand(I, NewIdx);
|
||||
// Clear the inbounds attribute because the new index may be off-bound.
|
||||
// e.g.,
|
||||
//
|
||||
// b = add i64 a, 5
|
||||
// addr = gep inbounds float* p, i64 b
|
||||
//
|
||||
// is transformed to:
|
||||
//
|
||||
// addr2 = gep float* p, i64 a
|
||||
// addr = gep float* addr2, i64 5
|
||||
//
|
||||
// If a is -4, although the old index b is in bounds, the new index a is
|
||||
// off-bound. http://llvm.org/docs/LangRef.html#id181 says "if the
|
||||
// inbounds keyword is not present, the offsets are added to the base
|
||||
// address with silently-wrapping two's complement arithmetic".
|
||||
// Therefore, the final code will be a semantically equivalent.
|
||||
//
|
||||
// TODO(jingyue): do some range analysis to keep as many inbounds as
|
||||
// possible. GEPs with inbounds are more friendly to alias analysis.
|
||||
GEP->setIsInBounds(false);
|
||||
Changed = true;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Offsets the base with the accumulative byte offset.
|
||||
//
|
||||
// %gep ; the base
|
||||
// ... %gep ...
|
||||
//
|
||||
// => add the offset
|
||||
//
|
||||
// %gep2 ; clone of %gep
|
||||
// %0 = ptrtoint %gep2
|
||||
// %1 = add %0, <offset>
|
||||
// %new.gep = inttoptr %1
|
||||
// %gep ; will be removed
|
||||
// ... %gep ...
|
||||
//
|
||||
// => replace all uses of %gep with %new.gep and remove %gep
|
||||
//
|
||||
// %gep2 ; clone of %gep
|
||||
// %0 = ptrtoint %gep2
|
||||
// %1 = add %0, <offset>
|
||||
// %new.gep = inttoptr %1
|
||||
// ... %new.gep ...
|
||||
//
|
||||
// TODO(jingyue): Emit a GEP instead of an "uglygep"
|
||||
// (http://llvm.org/docs/GetElementPtr.html#what-s-an-uglygep) to make the IR
|
||||
// prettier and more alias analysis friendly. One caveat: if the original GEP
|
||||
// ends with a StructType, we need to split the GEP at the last
|
||||
// SequentialType. For instance, consider the following IR:
|
||||
//
|
||||
// %struct.S = type { float, double }
|
||||
// @array = global [1024 x %struct.S]
|
||||
// %p = getelementptr %array, 0, %i + 5, 1
|
||||
//
|
||||
// To separate the constant 5 from %p, we would need to split %p at the last
|
||||
// array index so that we have:
|
||||
//
|
||||
// %addr = gep %array, 0, %i
|
||||
// %p = gep %addr, 5, 1
|
||||
Instruction *NewGEP = GEP->clone();
|
||||
NewGEP->insertBefore(GEP);
|
||||
Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
|
||||
Value *Addr = new PtrToIntInst(NewGEP, IntPtrTy, "", GEP);
|
||||
Addr = BinaryOperator::CreateAdd(
|
||||
Addr, ConstantInt::get(IntPtrTy, AccumulativeByteOffset, true), "", GEP);
|
||||
Addr = new IntToPtrInst(Addr, GEP->getType(), "", GEP);
|
||||
|
||||
GEP->replaceAllUsesWith(Addr);
|
||||
GEP->eraseFromParent();
|
||||
|
||||
return true;
|
||||
}
|
||||
|
||||
bool SeparateConstOffsetFromGEP::runOnFunction(Function &F) {
|
||||
if (DisableSeparateConstOffsetFromGEP)
|
||||
return false;
|
||||
|
||||
bool Changed = false;
|
||||
for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B) {
|
||||
for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ) {
|
||||
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I++)) {
|
||||
Changed |= splitGEP(GEP);
|
||||
}
|
||||
// No need to split GEP ConstantExprs because all its indices are constant
|
||||
// already.
|
||||
}
|
||||
}
|
||||
return Changed;
|
||||
}
|
||||
@ -0,0 +1,4 @@
|
||||
targets = set(config.root.targets_to_build.split())
|
||||
if not 'NVPTX' in targets:
|
||||
config.unsupported = True
|
||||
|
||||
@ -0,0 +1,60 @@
|
||||
; RUN: llc < %s -march=nvptx -mcpu=sm_20 | FileCheck %s --check-prefix=PTX
|
||||
; RUN: llc < %s -march=nvptx64 -mcpu=sm_20 | FileCheck %s --check-prefix=PTX
|
||||
; RUN: opt < %s -S -separate-const-offset-from-gep -gvn -dce | FileCheck %s --check-prefix=IR
|
||||
|
||||
; Verifies the SeparateConstOffsetFromGEP pass.
|
||||
; The following code computes
|
||||
; *output = array[x][y] + array[x][y+1] + array[x+1][y] + array[x+1][y+1]
|
||||
;
|
||||
; We expect SeparateConstOffsetFromGEP to transform it to
|
||||
;
|
||||
; float *base = &a[x][y];
|
||||
; *output = base[0] + base[1] + base[32] + base[33];
|
||||
;
|
||||
; so the backend can emit PTX that uses fewer virtual registers.
|
||||
|
||||
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
|
||||
target triple = "nvptx64-unknown-unknown"
|
||||
|
||||
@array = internal addrspace(3) constant [32 x [32 x float]] zeroinitializer, align 4
|
||||
|
||||
define void @sum_of_array(i32 %x, i32 %y, float* nocapture %output) {
|
||||
.preheader:
|
||||
%0 = zext i32 %y to i64
|
||||
%1 = zext i32 %x to i64
|
||||
%2 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %1, i64 %0
|
||||
%3 = addrspacecast float addrspace(3)* %2 to float*
|
||||
%4 = load float* %3, align 4
|
||||
%5 = fadd float %4, 0.000000e+00
|
||||
%6 = add i32 %y, 1
|
||||
%7 = zext i32 %6 to i64
|
||||
%8 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %1, i64 %7
|
||||
%9 = addrspacecast float addrspace(3)* %8 to float*
|
||||
%10 = load float* %9, align 4
|
||||
%11 = fadd float %5, %10
|
||||
%12 = add i32 %x, 1
|
||||
%13 = zext i32 %12 to i64
|
||||
%14 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %13, i64 %0
|
||||
%15 = addrspacecast float addrspace(3)* %14 to float*
|
||||
%16 = load float* %15, align 4
|
||||
%17 = fadd float %11, %16
|
||||
%18 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %13, i64 %7
|
||||
%19 = addrspacecast float addrspace(3)* %18 to float*
|
||||
%20 = load float* %19, align 4
|
||||
%21 = fadd float %17, %20
|
||||
store float %21, float* %output, align 4
|
||||
ret void
|
||||
}
|
||||
|
||||
; PTX-LABEL: sum_of_array(
|
||||
; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG:%(rl|r)[0-9]+]]{{\]}}
|
||||
; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG]]+4{{\]}}
|
||||
; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG]]+128{{\]}}
|
||||
; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG]]+132{{\]}}
|
||||
|
||||
; IR-LABEL: @sum_of_array(
|
||||
; IR: [[BASE_PTR:%[0-9]+]] = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i32 %x, i32 %y
|
||||
; IR: [[BASE_INT:%[0-9]+]] = ptrtoint float addrspace(3)* [[BASE_PTR]] to i64
|
||||
; IR: %5 = add i64 [[BASE_INT]], 4
|
||||
; IR: %10 = add i64 [[BASE_INT]], 128
|
||||
; IR: %15 = add i64 [[BASE_INT]], 132
|
||||
101
test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
Normal file
101
test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
Normal file
@ -0,0 +1,101 @@
|
||||
; RUN: opt < %s -separate-const-offset-from-gep -dce -S | FileCheck %s
|
||||
|
||||
; Several unit tests for -separate-const-offset-from-gep. The transformation
|
||||
; heavily relies on TargetTransformInfo, so we put these tests under
|
||||
; target-specific folders.
|
||||
|
||||
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
|
||||
; target triple is necessary; otherwise TargetTransformInfo rejects any
|
||||
; addressing mode.
|
||||
target triple = "nvptx64-unknown-unknown"
|
||||
|
||||
%struct.S = type { float, double }
|
||||
|
||||
@struct_array = global [1024 x %struct.S] zeroinitializer, align 16
|
||||
@float_2d_array = global [32 x [32 x float]] zeroinitializer, align 4
|
||||
|
||||
; We should not extract any struct field indices, because fields in a struct
|
||||
; may have different types.
|
||||
define double* @struct(i32 %i) {
|
||||
entry:
|
||||
%add = add nsw i32 %i, 5
|
||||
%idxprom = sext i32 %add to i64
|
||||
%p = getelementptr inbounds [1024 x %struct.S]* @struct_array, i64 0, i64 %idxprom, i32 1
|
||||
ret double* %p
|
||||
}
|
||||
; CHECK-LABEL: @struct
|
||||
; CHECK: getelementptr [1024 x %struct.S]* @struct_array, i64 0, i32 %i, i32 1
|
||||
|
||||
; We should be able to trace into sext/zext if it's directly used as a GEP
|
||||
; index.
|
||||
define float* @sext_zext(i32 %i, i32 %j) {
|
||||
entry:
|
||||
%i1 = add i32 %i, 1
|
||||
%j2 = add i32 %j, 2
|
||||
%i1.ext = sext i32 %i1 to i64
|
||||
%j2.ext = zext i32 %j2 to i64
|
||||
%p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i1.ext, i64 %j2.ext
|
||||
ret float* %p
|
||||
}
|
||||
; CHECK-LABEL: @sext_zext
|
||||
; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i32 %i, i32 %j
|
||||
; CHECK: add i64 %{{[0-9]+}}, 136
|
||||
|
||||
; We should be able to trace into sext/zext if it can be distributed to both
|
||||
; operands, e.g., sext (add nsw a, b) == add nsw (sext a), (sext b)
|
||||
define float* @ext_add_no_overflow(i64 %a, i32 %b, i64 %c, i32 %d) {
|
||||
%b1 = add nsw i32 %b, 1
|
||||
%b2 = sext i32 %b1 to i64
|
||||
%i = add i64 %a, %b2
|
||||
%d1 = add nuw i32 %d, 1
|
||||
%d2 = zext i32 %d1 to i64
|
||||
%j = add i64 %c, %d2
|
||||
%p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i, i64 %j
|
||||
ret float* %p
|
||||
}
|
||||
; CHECK-LABEL: @ext_add_no_overflow
|
||||
; CHECK: [[BASE_PTR:%[0-9]+]] = getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %{{[0-9]+}}, i64 %{{[0-9]+}}
|
||||
; CHECK: [[BASE_INT:%[0-9]+]] = ptrtoint float* [[BASE_PTR]] to i64
|
||||
; CHECK: add i64 [[BASE_INT]], 132
|
||||
|
||||
; We should treat "or" with no common bits (%k) as "add", and leave "or" with
|
||||
; potentially common bits (%l) as is.
|
||||
define float* @or(i64 %i) {
|
||||
entry:
|
||||
%j = shl i64 %i, 2
|
||||
%k = or i64 %j, 3 ; no common bits
|
||||
%l = or i64 %j, 4 ; potentially common bits
|
||||
%p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %k, i64 %l
|
||||
ret float* %p
|
||||
}
|
||||
; CHECK-LABEL: @or
|
||||
; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %j, i64 %l
|
||||
; CHECK: add i64 %{{[0-9]+}}, 384
|
||||
|
||||
; The subexpression (b + 5) is used in both "i = a + (b + 5)" and "*out = b +
|
||||
; 5". When extracting the constant offset 5, make sure "*out = b + 5" isn't
|
||||
; affected.
|
||||
define float* @expr(i64 %a, i64 %b, i64* %out) {
|
||||
entry:
|
||||
%b5 = add i64 %b, 5
|
||||
%i = add i64 %b5, %a
|
||||
%p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i, i64 0
|
||||
store i64 %b5, i64* %out
|
||||
ret float* %p
|
||||
}
|
||||
; CHECK-LABEL: @expr
|
||||
; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %0, i64 0
|
||||
; CHECK: add i64 %{{[0-9]+}}, 640
|
||||
; CHECK: store i64 %b5, i64* %out
|
||||
|
||||
; Verifies we handle "sub" correctly.
|
||||
define float* @sub(i64 %i, i64 %j) {
|
||||
%i2 = sub i64 %i, 5 ; i - 5
|
||||
%j2 = sub i64 5, %j ; 5 - i
|
||||
%p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i2, i64 %j2
|
||||
ret float* %p
|
||||
}
|
||||
; CHECK-LABEL: @sub
|
||||
; CHECK: %[[j2:[0-9]+]] = sub i64 0, %j
|
||||
; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i, i64 %[[j2]]
|
||||
; CHECK: add i64 %{{[0-9]+}}, -620
|
||||
Loading…
Reference in New Issue
Block a user