Commit 8dd9a136 authored by Nikita Popov's avatar Nikita Popov
Browse files

[InstCombine] Preserve inbounds when merging with zero-index GEP (PR44423) 

This addresses https://bugs.llvm.org/show_bug.cgi?id=44423.
If one of the GEPs is inbounds and the other is zero-index,
we can also preserve inbounds.

Differential Revision: https://reviews.llvm.org/D72060
parent 8dbe2f02

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

+11 −2
Original line number Diff line number Diff line
@@ -1649,6 +1649,15 @@ Instruction *InstCombiner::narrowMathIfNoOverflow(BinaryOperator &BO) { 
  return CastInst::Create(CastOpc, NarrowBO, BO.getType());

}



bool isMergedGEPInBounds(GEPOperator &GEP1, GEPOperator &GEP2) {

  // At least one GEP must be inbounds.

  if (!GEP1.isInBounds() && !GEP2.isInBounds())

    return false;



  return (GEP1.isInBounds() || GEP1.hasAllZeroIndices()) &&

         (GEP2.isInBounds() || GEP2.hasAllZeroIndices());

}



Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {

  SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());

  Type *GEPType = GEP.getType();
@@ -1922,7 +1931,7 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) { 


      // Update the GEP in place if possible.

      if (Src->getNumOperands() == 2) {

        GEP.setIsInBounds(GEP.isInBounds() && Src->isInBounds());

        GEP.setIsInBounds(isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP)));

        GEP.setOperand(0, Src->getOperand(0));

        GEP.setOperand(1, Sum);

        return &GEP;
@@ -1939,7 +1948,7 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) { 
    }



    if (!Indices.empty())

      return GEP.isInBounds() && Src->isInBounds()

      return isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP))

                 ? GetElementPtrInst::CreateInBounds(

                       Src->getSourceElementType(), Src->getOperand(0), Indices,

                       GEP.getName())

llvm/test/Transforms/InstCombine/getelementptr.ll

+3 −3
Original line number Diff line number Diff line
@@ -1171,7 +1171,7 @@ define <2 x i32*> @PR32414(i32** %ptr) { 


define i32* @test_bitcast_nzgep([1 x i32]* %base, i64 %idx) {

; CHECK-LABEL: @test_bitcast_nzgep(

; CHECK-NEXT:    [[PTR:%.*]] = getelementptr [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]

; CHECK-NEXT:    [[PTR:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]

; CHECK-NEXT:    ret i32* [[PTR]]

;

  %base2 = bitcast [1 x i32]* %base to i32*
@@ -1181,7 +1181,7 @@ define i32* @test_bitcast_nzgep([1 x i32]* %base, i64 %idx) { 


define i32* @test_zgep_nzgep([1 x i32]* %base, i64 %idx) {

; CHECK-LABEL: @test_zgep_nzgep(

; CHECK-NEXT:    [[PTR:%.*]] = getelementptr [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]

; CHECK-NEXT:    [[PTR:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]

; CHECK-NEXT:    ret i32* [[PTR]]

;

  %base2 = getelementptr [1 x i32], [1 x i32]* %base, i64 0, i64 0
@@ -1191,7 +1191,7 @@ define i32* @test_zgep_nzgep([1 x i32]* %base, i64 %idx) { 


define i32* @test_nzgep_zgep([1 x i32]* %base, i64 %idx) {

; CHECK-LABEL: @test_nzgep_zgep(

; CHECK-NEXT:    [[PTR:%.*]] = getelementptr [1 x i32], [1 x i32]* [[BASE:%.*]], i64 [[IDX:%.*]], i64 0

; CHECK-NEXT:    [[PTR:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[BASE:%.*]], i64 [[IDX:%.*]], i64 0

; CHECK-NEXT:    ret i32* [[PTR]]

;

  %base2 = getelementptr inbounds [1 x i32], [1 x i32]* %base, i64 %idx