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This intrinsic takes two arguments, ``%ptr`` and ``%offset``. It loads a 32-bit value from the address ``%ptr + %offset``, adds ``%ptr`` to that value and returns it. The constant folder specifically recognizes the form of this intrinsic and the constant initializers it may load from; if a loaded constant initializer is known to have the form ``i32 trunc(x - %ptr)``, the intrinsic call is folded to ``x``. LLVM provides that the calculation of such a constant initializer will not overflow at link time under the medium code model if ``x`` is an ``unnamed_addr`` function. However, it does not provide this guarantee for a constant initializer folded into a function body. This intrinsic can be used to avoid the possibility of overflows when loading from such a constant. Differential Revision: http://reviews.llvm.org/D18367 llvm-svn: 267223
86 lines
2.2 KiB
C++
86 lines
2.2 KiB
C++
//===-- PreISelIntrinsicLowering.cpp - Pre-ISel intrinsic lowering pass ---===//
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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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// This pass implements IR lowering for the llvm.load.relative intrinsic.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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using namespace llvm;
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namespace {
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bool lowerLoadRelative(Function &F) {
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if (F.use_empty())
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return false;
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bool Changed = false;
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Type *Int32Ty = Type::getInt32Ty(F.getContext());
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Type *Int32PtrTy = Int32Ty->getPointerTo();
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Type *Int8Ty = Type::getInt8Ty(F.getContext());
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for (auto I = F.use_begin(), E = F.use_end(); I != E;) {
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auto CI = dyn_cast<CallInst>(I->getUser());
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++I;
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if (!CI || CI->getCalledValue() != &F)
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continue;
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IRBuilder<> B(CI);
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Value *OffsetPtr =
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B.CreateGEP(Int8Ty, CI->getArgOperand(0), CI->getArgOperand(1));
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Value *OffsetPtrI32 = B.CreateBitCast(OffsetPtr, Int32PtrTy);
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Value *OffsetI32 = B.CreateAlignedLoad(OffsetPtrI32, 4);
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Value *ResultPtr = B.CreateGEP(Int8Ty, CI->getArgOperand(0), OffsetI32);
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CI->replaceAllUsesWith(ResultPtr);
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CI->eraseFromParent();
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Changed = true;
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}
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return Changed;
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}
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bool lowerIntrinsics(Module &M) {
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bool Changed = false;
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for (Function &F : M) {
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if (F.getName().startswith("llvm.load.relative."))
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Changed |= lowerLoadRelative(F);
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}
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return Changed;
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}
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class PreISelIntrinsicLowering : public ModulePass {
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public:
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static char ID;
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PreISelIntrinsicLowering() : ModulePass(ID) {}
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bool runOnModule(Module &M) {
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return lowerIntrinsics(M);
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}
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};
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char PreISelIntrinsicLowering::ID;
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}
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INITIALIZE_PASS(PreISelIntrinsicLowering, "pre-isel-intrinsic-lowering",
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"Pre-ISel Intrinsic Lowering", false, false)
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ModulePass *llvm::createPreISelIntrinsicLoweringPass() {
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return new PreISelIntrinsicLowering;
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}
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