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[InstCombine][foldPHIArgGEPIntoPHI] Early return for const vector index for gep inst. #138661

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Merged
merged 4 commits into from
May 8, 2025
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[InstCombine][foldPHIArgGEPIntoPHI] Early return for const vector index for gep inst. #138661

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[InstCombine][foldPHIArgGEPIntoPHI] Early return for const vector ind…
haonanya1 May 6, 2025
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4 changes: 2 additions & 2 deletions llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -574,8 +574,8 @@ Instruction *InstCombinerImpl::foldPHIArgGEPIntoPHI(PHINode &PN) {
// substantially cheaper to compute for the constants, so making it a
// variable index could pessimize the path. This also handles the case
// for struct indices, which must always be constant.
if (isa<ConstantInt>(FirstInst->getOperand(Op)) ||
isa<ConstantInt>(GEP->getOperand(Op)))
if (isa<Constant>(FirstInst->getOperand(Op)) ||
isa<Constant>(GEP->getOperand(Op)))
return nullptr;

if (FirstInst->getOperand(Op)->getType() !=
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43 changes: 43 additions & 0 deletions llvm/test/Transforms/InstCombine/fold-phi-arg-gep-to-phi-negative.ll
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This ended up a bit too reduced now and no longer crashes without the change. This variant works:

%foo = type { i16, i16, i16 }

define <16 x ptr> @test(i1 %tobool) {
entry:
  %lane.0 = alloca %foo, align 16
  %lane.15 = insertelement <16 x ptr> poison, ptr %lane.0, i64 0
  %mm_vectorGEP = getelementptr inbounds %foo, <16 x ptr> %lane.15, <16 x i64> zeroinitializer, <16 x i32> splat (i32 1)
  %mm_vectorGEP2 = getelementptr inbounds %foo, <16 x ptr> %lane.15, <16 x i64> zeroinitializer, <16 x i32> splat (i32 2)
  br i1 %tobool, label %f1, label %f0

f0:
  br label %merge

f1:
  br label %merge

merge:
  %vec.phi = phi <16 x ptr> [ %mm_vectorGEP, %f0], [ %mm_vectorGEP2, %f1 ]
  ret <16 x ptr> %vec.phi
}

(This makes sure the second GEP is not optimized away.)

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Thanks for your patience, updated.

Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

%vec = type { %vec_base }
%vec_base = type { [4 x float] }
%foo = type { %vec, %vec}
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It is possible to simplify the GEP type a bit? I don't think you need all of these levels of nesting. All you really need is a struct index using a vector.

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done, thanks.


define void @test(i1 %tobool, ptr addrspace(1) %add.ptr) {
; CHECK-LABEL: define void @test(
; CHECK-SAME: i1 [[TOBOOL:%.*]], ptr addrspace(1) [[ADD_PTR:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[LANE_0:%.*]] = alloca [[FOO:%.*]], align 16
; CHECK-NEXT: [[LANE_15:%.*]] = insertelement <16 x ptr> poison, ptr [[LANE_0]], i64 0
; CHECK-NEXT: br i1 [[TOBOOL]], label %[[F1:.*]], label %[[F0:.*]]
; CHECK: [[F0]]:
; CHECK-NEXT: [[MM_VECTORGEP:%.*]] = getelementptr inbounds [[FOO]], <16 x ptr> [[LANE_15]], <16 x i64> zeroinitializer, <16 x i32> splat (i32 1), <16 x i32> zeroinitializer, <16 x i32> zeroinitializer, <16 x i64> splat (i64 1)
; CHECK-NEXT: br label %[[MERGE:.*]]
; CHECK: [[F1]]:
; CHECK-NEXT: [[MM_VECTORGEP2:%.*]] = getelementptr inbounds [[FOO]], <16 x ptr> [[LANE_15]], <16 x i64> zeroinitializer, <16 x i32> zeroinitializer, <16 x i32> zeroinitializer, <16 x i32> zeroinitializer, <16 x i64> splat (i64 1)
; CHECK-NEXT: br label %[[MERGE]]
; CHECK: [[MERGE]]:
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <16 x ptr> [ [[MM_VECTORGEP]], %[[F0]] ], [ [[MM_VECTORGEP2]], %[[F1]] ]
; CHECK-NEXT: store <16 x ptr> [[VEC_PHI]], ptr addrspace(1) [[ADD_PTR]], align 128
; CHECK-NEXT: ret void
;
entry:
%lane.0 = alloca %foo, align 16
%lane.15 = insertelement <16 x ptr> poison, ptr %lane.0, i64 0
%mm_vectorGEP = getelementptr inbounds %foo, <16 x ptr> %lane.15, <16 x i64> zeroinitializer, <16 x i32> splat (i32 1), <16 x i32> zeroinitializer, <16 x i32> zeroinitializer, <16 x i64> splat (i64 1)
%mm_vectorGEP2 = getelementptr inbounds %foo, <16 x ptr> %lane.15, <16 x i64> zeroinitializer, <16 x i32> zeroinitializer, <16 x i32> zeroinitializer, <16 x i32> zeroinitializer, <16 x i64> splat (i64 1)
br i1 %tobool, label %f1, label %f0

f0:
br label %merge

f1:
br label %merge

merge:
%vec.phi = phi <16 x ptr> [ %mm_vectorGEP, %f0], [ %mm_vectorGEP2, %f1 ]
store <16 x ptr> %vec.phi, ptr addrspace(1) %add.ptr
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Can replace the store with a return.

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done, thanks.

ret void
}
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