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[NaryReassociate] Run EarlyCSE after NaryReassociate

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Summary:
This patch made two improvements to NaryReassociate and the NVPTX pipeline

1. Run EarlyCSE/GVN after NaryReassociate to get rid of redundant common
expressions.

2. When adding an instruction to SeenExprs, maps both the SCEV before and after
reassociation to that instruction.

Test Plan: updated @reassociate_gep_nsw in nary-gep.ll

Reviewers: meheff, broune

Reviewed By: broune

Subscribers: dberlin, jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D9947

llvm-svn: 238396
This commit is contained in:
Jingyue Wu 2015-05-28 04:56:52 +00:00
parent 521fdf1acb
commit 6c391c6619
3 changed files with 48 additions and 10 deletions
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3
lib/Target/NVPTX/NVPTXTargetMachine.cpp
View File

@ -181,6 +181,9 @@ void NVPTXPassConfig::addIRPasses() {
addPass(createEarlyCSEPass());
// Run NaryReassociate after EarlyCSE/GVN to be more effective.
addPass(createNaryReassociatePass());
// NaryReassociate on GEPs creates redundant common expressions, so run
// EarlyCSE after it.
addPass(createEarlyCSEPass());
}
bool NVPTXPassConfig::addInstSelector() {

24
lib/Transforms/Scalar/NaryReassociate.cpp
View File

@ -234,6 +234,7 @@ bool NaryReassociate::doOneIteration(Function &F) {
BasicBlock *BB = Node->getBlock();
for (auto I = BB->begin(); I != BB->end(); ++I) {
if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(I)) {
const SCEV *OldSCEV = SE->getSCEV(I);
if (Instruction *NewI = tryReassociate(I)) {
Changed = true;
SE->forgetValue(I);
@ -243,7 +244,28 @@ bool NaryReassociate::doOneIteration(Function &F) {
}
// Add the rewritten instruction to SeenExprs; the original instruction
// is deleted.
SeenExprs[SE->getSCEV(I)].push_back(I);
const SCEV *NewSCEV = SE->getSCEV(I);
SeenExprs[NewSCEV].push_back(I);
// Ideally, NewSCEV should equal OldSCEV because tryReassociate(I)
// is equivalent to I. However, ScalarEvolution::getSCEV may
// weaken nsw causing NewSCEV not to equal OldSCEV. For example, suppose
// we reassociate
// I = &a[sext(i +nsw j)] // assuming sizeof(a[0]) = 4
// to
// NewI = &a[sext(i)] + sext(j).
//
// ScalarEvolution computes
// getSCEV(I) = a + 4 * sext(i + j)
// getSCEV(newI) = a + 4 * sext(i) + 4 * sext(j)
// which are different SCEVs.
//
// To alleviate this issue of ScalarEvolution not always capturing
// equivalence, we add I to SeenExprs[OldSCEV] as well so that we can
// map both SCEV before and after tryReassociate(I) to I.
//
// This improvement is exercised in @reassociate_gep_nsw in nary-gep.ll.
if (NewSCEV != OldSCEV)
SeenExprs[OldSCEV].push_back(I);
}
}
}

31
test/Transforms/NaryReassociate/NVPTX/nary-gep.ll
View File

@ -1,4 +1,4 @@
; RUN: opt < %s -nary-reassociate -S | FileCheck %s
; RUN: opt < %s -nary-reassociate -early-cse -S | FileCheck %s
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
target triple = "nvptx64-unknown-unknown"
@ -27,24 +27,37 @@ define void @reassociate_gep(float* %a, i64 %i, i64 %j) {
; foo(&a[sext(j)]);
; foo(&a[sext(i +nsw j)]);
; foo(&a[sext((i +nsw j) +nsw i)]);
; =>
; t = &a[sext(j)];
; foo(t);
; foo(t + sext(i));
; t1 = &a[sext(j)];
; foo(t1);
; t2 = t1 + sext(i);
; foo(t2);
; t3 = t2 + sext(i); // sext(i) should be GVN'ed.
; foo(t3);
define void @reassociate_gep_nsw(float* %a, i32 %i, i32 %j) {
; CHECK-LABEL: @reassociate_gep_nsw(
%1 = add nsw i32 %i, %j
%idxprom.1 = sext i32 %1 to i64
%idxprom.j = sext i32 %j to i64
%2 = getelementptr float, float* %a, i64 %idxprom.j
%1 = getelementptr float, float* %a, i64 %idxprom.j
; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i64 %idxprom.j
call void @foo(float* %2)
call void @foo(float* %1)
; CHECK: call void @foo(float* [[t1]])
%3 = getelementptr float, float* %a, i64 %idxprom.1
%2 = add nsw i32 %i, %j
%idxprom.2 = sext i32 %2 to i64
%3 = getelementptr float, float* %a, i64 %idxprom.2
; CHECK: [[sexti:[^ ]+]] = sext i32 %i to i64
; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 [[sexti]]
call void @foo(float* %3)
; CHECK: call void @foo(float* [[t2]])
%4 = add nsw i32 %2, %i
%idxprom.4 = sext i32 %4 to i64
%5 = getelementptr float, float* %a, i64 %idxprom.4
; CHECK: [[t3:[^ ]+]] = getelementptr float, float* [[t2]], i64 [[sexti]]
call void @foo(float* %5)
; CHECK: call void @foo(float* [[t3]])
ret void
}