[llvm] r209049 - Add support for combining GEPs across PHI nodes
Louis Gerbarg
lgg at apple.com
Fri May 16 16:47:25 PDT 2014
Author: louis
Date: Fri May 16 18:47:24 2014
New Revision: 209049
URL: http://llvm.org/viewvc/llvm-project?rev=209049&view=rev
Log:
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.
rdar://15547484
Added:
llvm/trunk/test/Transforms/InstCombine/gepphigep.ll
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=209049&r1=209048&r2=209049&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Fri May 16 18:47:24 2014
@@ -1220,6 +1220,65 @@ Instruction *InstCombiner::visitGetEleme
if (MadeChange) return &GEP;
}
+ // Check to see if the inputs to the PHI node are getelementptr instructions.
+ if (PHINode *PN = dyn_cast<PHINode>(PtrOp)) {
+ GetElementPtrInst *Op1 = dyn_cast<GetElementPtrInst>(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<GetElementPtrInst>(*I);
+ if (!Op2 || Op1->getNumOperands() != Op1->getNumOperands())
+ return nullptr;
+
+ for (unsigned J = 0, F = Op1->getNumOperands(); J != F; ++J) {
+ 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.
+ 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 = dyn_cast<GetElementPtrInst>(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.
+ PHINode *NewPN = Builder->CreatePHI(Op1->getOperand(DI)->getType(),
+ PN->getNumOperands());
+ for (auto &I : PN->operands())
+ NewPN->addIncoming(dyn_cast<GEPOperator>(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.
Added: llvm/trunk/test/Transforms/InstCombine/gepphigep.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/gepphigep.ll?rev=209049&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/gepphigep.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/gepphigep.ll Fri May 16 18:47:24 2014
@@ -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
+}
+
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