Author: Nikita Popov Date: 2020-12-23T21:41:53+01:00 New Revision: eb79fd3c928dbbb97f7937963361c1dad2bf8222
URL: https://github.com/llvm/llvm-project/commit/eb79fd3c928dbbb97f7937963361c1dad2bf8222 DIFF: https://github.com/llvm/llvm-project/commit/eb79fd3c928dbbb97f7937963361c1dad2bf8222.diff LOG: [InstCombine] Fold gep inbounds of null to null Effectively, this is what we were previously already doing when the GEP was used in conjunction with a load or store, but this fold can also be applied more generally: > The only in bounds address for a null pointer in the default > address-space is the null pointer itself. Added: Modified: llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp llvm/lib/Transforms/InstCombine/InstructionCombining.cpp llvm/test/Transforms/InstCombine/getelementptr.ll llvm/test/Transforms/InstCombine/store.ll Removed: ################################################################################ diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp index 71f165abe52e..153947802f80 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp @@ -903,29 +903,14 @@ static Instruction *replaceGEPIdxWithZero(InstCombinerImpl &IC, Value *Ptr, } static bool canSimplifyNullStoreOrGEP(StoreInst &SI) { - if (NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace())) - return false; - - auto *Ptr = SI.getPointerOperand(); - if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) - if (GEPI->isInBounds()) - Ptr = GEPI->getOperand(0); - return (isa<ConstantPointerNull>(Ptr) && - !NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace())); + return isa<ConstantPointerNull>(SI.getPointerOperand()) && + !NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace()); } static bool canSimplifyNullLoadOrGEP(LoadInst &LI, Value *Op) { - if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) { - const Value *GEPI0 = GEPI->getOperand(0); - if (isa<ConstantPointerNull>(GEPI0) && GEPI->isInBounds() && - !NullPointerIsDefined(LI.getFunction(), GEPI->getPointerAddressSpace())) - return true; - } - if (isa<UndefValue>(Op) || - (isa<ConstantPointerNull>(Op) && - !NullPointerIsDefined(LI.getFunction(), LI.getPointerAddressSpace()))) - return true; - return false; + return isa<UndefValue>(Op) || + (isa<ConstantPointerNull>(Op) && + !NullPointerIsDefined(LI.getFunction(), LI.getPointerAddressSpace())); } Instruction *InstCombinerImpl::visitLoadInst(LoadInst &LI) { diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp index ec932aaf0b9e..7bde3845522f 100644 --- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -1855,6 +1855,12 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) { Value *PtrOp = GEP.getOperand(0); + // The only pointer that is inbounds of null is null. + if (isa<ConstantPointerNull>(PtrOp) && GEP.isInBounds() && + !NullPointerIsDefined(GEP.getFunction(), + PtrOp->getType()->getPointerAddressSpace())) + return replaceInstUsesWith(GEP, PtrOp); + // Eliminate unneeded casts for indices, and replace indices which displace // by multiples of a zero size type with zero. bool MadeChange = false; diff --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll index b4124c5edf5e..6524c3c03639 100644 --- a/llvm/test/Transforms/InstCombine/getelementptr.ll +++ b/llvm/test/Transforms/InstCombine/getelementptr.ll @@ -1239,8 +1239,7 @@ define i32* @PR45084_extra_use(i1 %cond, %struct.f** %p) { define i8* @gep_null_inbounds(i64 %idx) { ; CHECK-LABEL: @gep_null_inbounds( -; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, i8* null, i64 [[IDX:%.*]] -; CHECK-NEXT: ret i8* [[GEP]] +; CHECK-NEXT: ret i8* null ; %gep = getelementptr inbounds i8, i8* null, i64 %idx ret i8* %gep diff --git a/llvm/test/Transforms/InstCombine/store.ll b/llvm/test/Transforms/InstCombine/store.ll index d3842f4bb469..a94ce92d214e 100644 --- a/llvm/test/Transforms/InstCombine/store.ll +++ b/llvm/test/Transforms/InstCombine/store.ll @@ -25,8 +25,7 @@ define void @test2(i32* %P) { define void @store_at_gep_off_null_inbounds(i64 %offset) { ; CHECK-LABEL: @store_at_gep_off_null_inbounds( -; CHECK-NEXT: [[PTR:%.*]] = getelementptr inbounds i32, i32* null, i64 [[OFFSET:%.*]] -; CHECK-NEXT: store i32 undef, i32* [[PTR]], align 4 +; CHECK-NEXT: store i32 undef, i32* null, align 536870912 ; CHECK-NEXT: ret void ; %ptr = getelementptr inbounds i32, i32 *null, i64 %offset _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
