From 727f1cbb1770b860df9293563a1c957f47215ec6 Mon Sep 17 00:00:00 2001 From: Louis Gerbarg Date: Wed, 28 May 2014 17:38:31 +0000 Subject: [PATCH] Add support for combining GEPs across PHI nodes Currently LLVM will generally merge GEPs. This allows backends to use more complex addressing modes. In some cases this is not happening because there is PHI inbetween the two GEPs: GEP1--\ |-->PHI1-->GEP3 GEP2--/ This patch checks to see if GEP1 and GEP2 are similiar enough that they can be cloned (GEP12) in GEP3's BB, allowing GEP->GEP merging (GEP123): GEP1--\ --\ --\ |-->PHI1-->GEP3 ==> |-->PHI2->GEP12->GEP3 == > |-->PHI2->GEP123 GEP2--/ --/ --/ This also breaks certain use chains that are preventing GEP->GEP merges that the the existing instcombine would merge otherwise. Tests included. llvm-svn: 209755 --- .../InstCombine/InstructionCombining.cpp | 79 ++++++++++++++++++++++ llvm/test/Transforms/InstCombine/gepphigep.ll | 56 +++++++++++++++ 2 files changed, 135 insertions(+) create mode 100644 llvm/test/Transforms/InstCombine/gepphigep.ll diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp index 4c36887..80eec1b 100644 --- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -1220,6 +1220,85 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) { if (MadeChange) return &GEP; } + // Check to see if the inputs to the PHI node are getelementptr instructions. + if (PHINode *PN = dyn_cast(PtrOp)) { + GetElementPtrInst *Op1 = dyn_cast(PN->getOperand(0)); + if (!Op1) + return nullptr; + + signed DI = -1; + + for (auto I = PN->op_begin()+1, E = PN->op_end(); I !=E; ++I) { + GetElementPtrInst *Op2 = dyn_cast(*I); + if (!Op2 || Op1->getNumOperands() != Op2->getNumOperands()) + return nullptr; + + for (unsigned J = 0, F = Op1->getNumOperands(); J != F; ++J) { + if (Op1->getOperand(J)->getType() != Op2->getOperand(J)->getType()) + return nullptr; + + if (Op1->getOperand(J) != Op2->getOperand(J)) { + if (DI == -1) { + // We have not seen any differences yet in the GEPs feeding the + // PHI yet, so we record this one if it is allowed to be a + // variable. + + // The first two arguments can vary for any GEP, the rest have to be + // static for struct slots + if (J > 1) { + SmallVector Idxs(GEP.idx_begin(), GEP.idx_begin()+J); + Type *Ty = + GetElementPtrInst::getIndexedType(Op1->getOperand(0)->getType(), + Idxs); + if (Ty->isStructTy()) + return nullptr; + } + + DI = J; + } else { + // The GEP is different by more than one input. While this could be + // extended to support GEPs that vary by more than one variable it + // doesn't make sense since it greatly increases the complexity and + // would result in an R+R+R addressing mode which no backend + // directly supports and would need to be broken into several + // simpler instructions anyway. + return nullptr; + } + } + } + } + + GetElementPtrInst *NewGEP = cast(Op1->clone()); + + if (DI == -1) { + // All the GEPs feeding the PHI are identical. Clone one down into our + // BB so that it can be merged with the current GEP. + GEP.getParent()->getInstList().insert(GEP.getParent()->getFirstNonPHI(), + NewGEP); + } else { + // All the GEPs feeding the PHI differ at a single offset. Clone a GEP + // into the current block so it can be merged, and create a new PHI to + // set that index. + Instruction *InsertPt = Builder->GetInsertPoint(); + Builder->SetInsertPoint(PN); + PHINode *NewPN = Builder->CreatePHI(Op1->getOperand(DI)->getType(), + PN->getNumOperands()); + Builder->SetInsertPoint(InsertPt); + + for (auto &I : PN->operands()) + NewPN->addIncoming(cast(I)->getOperand(DI), + PN->getIncomingBlock(I)); + + NewGEP->setOperand(DI, NewPN); + GEP.getParent()->getInstList().insert(GEP.getParent()->getFirstNonPHI(), + NewGEP); + NewGEP->setOperand(DI, NewPN); + } + + GEP.setOperand(0, NewGEP); + PtrOp = NewGEP; + } + // Combine Indices - If the source pointer to this getelementptr instruction // is a getelementptr instruction, combine the indices of the two // getelementptr instructions into a single instruction. diff --git a/llvm/test/Transforms/InstCombine/gepphigep.ll b/llvm/test/Transforms/InstCombine/gepphigep.ll new file mode 100644 index 0000000..9aab609 --- /dev/null +++ b/llvm/test/Transforms/InstCombine/gepphigep.ll @@ -0,0 +1,56 @@ +; RUN: opt -instcombine -S < %s | FileCheck %s + +%struct1 = type { %struct2*, i32, i32, i32 } +%struct2 = type { i32, i32 } + +define i32 @test1(%struct1* %dm, i1 %tmp4, i64 %tmp9, i64 %tmp19) { +bb: + %tmp = getelementptr inbounds %struct1* %dm, i64 0, i32 0 + %tmp1 = load %struct2** %tmp, align 8 + br i1 %tmp4, label %bb1, label %bb2 + +bb1: + %tmp10 = getelementptr inbounds %struct2* %tmp1, i64 %tmp9 + %tmp11 = getelementptr inbounds %struct2* %tmp10, i64 0, i32 0 + store i32 0, i32* %tmp11, align 4 + br label %bb3 + +bb2: + %tmp20 = getelementptr inbounds %struct2* %tmp1, i64 %tmp19 + %tmp21 = getelementptr inbounds %struct2* %tmp20, i64 0, i32 0 + store i32 0, i32* %tmp21, align 4 + br label %bb3 + +bb3: + %phi = phi %struct2* [ %tmp10, %bb1 ], [ %tmp20, %bb2 ] + %tmp24 = getelementptr inbounds %struct2* %phi, i64 0, i32 1 + %tmp25 = load i32* %tmp24, align 4 + ret i32 %tmp25 + +; CHECK-LABEL: @test1( +; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp9, i32 0 +; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp19, i32 0 +; CHECK: %[[PHI:[0-9A-Za-z]+]] = phi i64 [ %tmp9, %bb1 ], [ %tmp19, %bb2 ] +; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %[[PHI]], i32 1 + +} + +define i32 @test2(%struct1* %dm, i1 %tmp4, i64 %tmp9, i64 %tmp19) { +bb: + %tmp = getelementptr inbounds %struct1* %dm, i64 0, i32 0 + %tmp1 = load %struct2** %tmp, align 8 + %tmp10 = getelementptr inbounds %struct2* %tmp1, i64 %tmp9 + %tmp11 = getelementptr inbounds %struct2* %tmp10, i64 0, i32 0 + store i32 0, i32* %tmp11, align 4 + %tmp20 = getelementptr inbounds %struct2* %tmp1, i64 %tmp19 + %tmp21 = getelementptr inbounds %struct2* %tmp20, i64 0, i32 0 + store i32 0, i32* %tmp21, align 4 + %tmp24 = getelementptr inbounds %struct2* %tmp10, i64 0, i32 1 + %tmp25 = load i32* %tmp24, align 4 + ret i32 %tmp25 + +; CHECK-LABEL: @test2( +; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp9, i32 0 +; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp19, i32 0 +; CHECK: getelementptr inbounds %struct2* %tmp1, i64 %tmp9, i32 1 +} -- 2.7.4