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[instcombine] Scalarize operands of vector geps if possible #145402

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Jun 24, 2025
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[instcombine] Scalarize operands of vector geps if possible #145402

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6dfe466
[instcombine] Scalarize operands of vector geps if possible
preames Jun 23, 2025
a77a79f
Address review comments
preames Jun 24, 2025
0a620f0
Remove confusing todo for now
preames Jun 24, 2025
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30 changes: 26 additions & 4 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Expand Up @@ -2993,10 +2993,6 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
return replaceInstUsesWith(GEP, V);
return &GEP;
}

// TODO: 1) Scalarize splat operands, 2) scalarize entire instruction if
// possible (decide on canonical form for pointer broadcast), 3) exploit
// undef elements to decrease demanded bits
}

// Eliminate unneeded casts for indices, and replace indices which displace
Expand Down Expand Up @@ -3058,6 +3054,32 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
return replaceInstUsesWith(GEP, NewGEP);
}

// Scalarize vector operands; prefer splat-of-gep.as canonical form.
// Note that this looses information about undef lanes; we run it after
// demanded bits to partially mitigate that loss.
if (GEPType->isVectorTy() && llvm::any_of(GEP.operands(), [](Value *Op) {
return Op->getType()->isVectorTy() && getSplatValue(Op);
})) {
SmallVector<Value *> NewOps;
for (auto &Op : GEP.operands()) {
if (Op->getType()->isVectorTy())
if (Value *Scalar = getSplatValue(Op)) {
NewOps.push_back(Scalar);
continue;
}
NewOps.push_back(Op);
}

Value *Res = Builder.CreateGEP(GEP.getSourceElementType(), NewOps[0],
ArrayRef(NewOps).drop_front(), GEP.getName(),
GEP.getNoWrapFlags());
if (!Res->getType()->isVectorTy()) {
ElementCount EC = cast<VectorType>(GEPType)->getElementCount();
Res = Builder.CreateVectorSplat(EC, Res);
}
return replaceInstUsesWith(GEP, Res);
}

// Check to see if the inputs to the PHI node are getelementptr instructions.
if (auto *PN = dyn_cast<PHINode>(PtrOp)) {
if (Value *NewPtrOp = foldGEPOfPhi(GEP, PN, Builder))
Expand Down
6 changes: 3 additions & 3 deletions llvm/test/Transforms/InstCombine/fold-phi-arg-gep-to-phi-negative.ll
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Expand Up @@ -11,13 +11,13 @@ define <16 x ptr> @test(i1 %tobool) {
; 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)
; CHECK-NEXT: [[MM_VECTORGEP1:%.*]] = getelementptr inbounds i8, <16 x ptr> [[LANE_15]], i64 2
; 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> splat (i32 2)
; CHECK-NEXT: [[MM_VECTORGEP22:%.*]] = getelementptr inbounds i8, <16 x ptr> [[LANE_15]], i64 4
; CHECK-NEXT: br label %[[MERGE]]
; CHECK: [[MERGE]]:
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <16 x ptr> [ [[MM_VECTORGEP]], %[[F0]] ], [ [[MM_VECTORGEP2]], %[[F1]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <16 x ptr> [ [[MM_VECTORGEP1]], %[[F0]] ], [ [[MM_VECTORGEP22]], %[[F1]] ]
; CHECK-NEXT: ret <16 x ptr> [[VEC_PHI]]
;
entry:
Expand Down
10 changes: 5 additions & 5 deletions llvm/test/Transforms/InstCombine/getelementptr.ll
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Expand Up @@ -247,11 +247,11 @@ define <2 x i1> @test13_vector2(i64 %X, <2 x ptr> %P) nounwind {

define <2 x i1> @test13_fixed_fixed(i64 %X, ptr %P, <2 x i64> %y) nounwind {
; CHECK-LABEL: @test13_fixed_fixed(
; CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i64> poison, i64 [[X:%.*]], i64 0
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i64> [[DOTSPLATINSERT]], <i64 3, i64 0>
; CHECK-NEXT: [[A_IDX:%.*]] = shufflevector <2 x i64> [[TMP1]], <2 x i64> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: [[B_IDX:%.*]] = shl nsw <2 x i64> [[Y:%.*]], splat (i64 4)
; CHECK-NEXT: [[C:%.*]] = icmp eq <2 x i64> [[A_IDX]], [[B_IDX]]
; CHECK-NEXT: [[A1:%.*]] = getelementptr inbounds <2 x i64>, ptr [[P:%.*]], i64 0, i64 [[X:%.*]]
; CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x ptr> poison, ptr [[A1]], i64 0
; CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <2 x ptr> [[DOTSPLATINSERT]], <2 x ptr> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: [[B:%.*]] = getelementptr inbounds <2 x i64>, ptr [[P]], <2 x i64> [[Y:%.*]]
; CHECK-NEXT: [[C:%.*]] = icmp eq <2 x ptr> [[DOTSPLAT]], [[B]]
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Regression, as we don't look through splats in this transform. But I doubt this matters in practice.

; CHECK-NEXT: ret <2 x i1> [[C]]
;
%A = getelementptr inbounds <2 x i64>, ptr %P, <2 x i64> zeroinitializer, i64 %X
Expand Down
24 changes: 9 additions & 15 deletions llvm/test/Transforms/InstCombine/vec_demanded_elts-inseltpoison.ll
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Expand Up @@ -525,9 +525,7 @@ define ptr @gep_splat_base_w_s_idx(ptr %base) {

define ptr @gep_splat_base_w_cv_idx(ptr %base) {
; CHECK-LABEL: @gep_splat_base_w_cv_idx(
; CHECK-NEXT: [[BASEVEC2:%.*]] = insertelement <2 x ptr> poison, ptr [[BASE:%.*]], i64 1
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, <2 x ptr> [[BASEVEC2]], <2 x i64> <i64 poison, i64 1>
; CHECK-NEXT: [[EE:%.*]] = extractelement <2 x ptr> [[GEP]], i64 1
; CHECK-NEXT: [[EE:%.*]] = getelementptr i8, ptr [[BASE:%.*]], i64 4
; CHECK-NEXT: ret ptr [[EE]]
;
%basevec1 = insertelement <2 x ptr> poison, ptr %base, i32 0
Expand All @@ -539,9 +537,8 @@ define ptr @gep_splat_base_w_cv_idx(ptr %base) {

define ptr @gep_splat_base_w_vidx(ptr %base, <2 x i64> %idxvec) {
; CHECK-LABEL: @gep_splat_base_w_vidx(
; CHECK-NEXT: [[BASEVEC2:%.*]] = insertelement <2 x ptr> poison, ptr [[BASE:%.*]], i64 1
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, <2 x ptr> [[BASEVEC2]], <2 x i64> [[IDXVEC:%.*]]
; CHECK-NEXT: [[EE:%.*]] = extractelement <2 x ptr> [[GEP]], i64 1
; CHECK-NEXT: [[TMP1:%.*]] = extractelement <2 x i64> [[IDXVEC:%.*]], i64 1
; CHECK-NEXT: [[EE:%.*]] = getelementptr i32, ptr [[BASE:%.*]], i64 [[TMP1]]
; CHECK-NEXT: ret ptr [[EE]]
;
%basevec1 = insertelement <2 x ptr> poison, ptr %base, i32 0
Expand Down Expand Up @@ -597,10 +594,7 @@ define ptr @gep_sbase_w_splat_idx(ptr %base, i64 %idx) {
}
define ptr @gep_splat_both(ptr %base, i64 %idx) {
; CHECK-LABEL: @gep_splat_both(
; CHECK-NEXT: [[BASEVEC2:%.*]] = insertelement <2 x ptr> poison, ptr [[BASE:%.*]], i64 1
; CHECK-NEXT: [[IDXVEC2:%.*]] = insertelement <2 x i64> poison, i64 [[IDX:%.*]], i64 1
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, <2 x ptr> [[BASEVEC2]], <2 x i64> [[IDXVEC2]]
; CHECK-NEXT: [[EE:%.*]] = extractelement <2 x ptr> [[GEP]], i64 1
; CHECK-NEXT: [[EE:%.*]] = getelementptr i32, ptr [[BASE:%.*]], i64 [[IDX:%.*]]
; CHECK-NEXT: ret ptr [[EE]]
;
%basevec1 = insertelement <2 x ptr> poison, ptr %base, i32 0
Expand Down Expand Up @@ -641,9 +635,9 @@ define ptr @gep_demanded_lane_undef(ptr %base, i64 %idx) {
;; indices.
define ptr @PR41624(<2 x ptr> %a) {
; CHECK-LABEL: @PR41624(
; CHECK-NEXT: [[W:%.*]] = getelementptr { i32, i32 }, <2 x ptr> [[A:%.*]], <2 x i64> splat (i64 5), <2 x i32> zeroinitializer
; CHECK-NEXT: [[R:%.*]] = extractelement <2 x ptr> [[W]], i64 0
; CHECK-NEXT: ret ptr [[R]]
; CHECK-NEXT: [[R:%.*]] = extractelement <2 x ptr> [[W:%.*]], i64 0
; CHECK-NEXT: [[R1:%.*]] = getelementptr i8, ptr [[R]], i64 40
; CHECK-NEXT: ret ptr [[R1]]
;
%w = getelementptr { i32, i32 }, <2 x ptr> %a, <2 x i64> <i64 5, i64 5>, <2 x i32> zeroinitializer
%r = extractelement <2 x ptr> %w, i32 0
Expand All @@ -657,8 +651,8 @@ define ptr @PR41624(<2 x ptr> %a) {
define ptr @zero_sized_type_extract(<4 x i64> %arg, i64 %arg1) {
; CHECK-LABEL: @zero_sized_type_extract(
; CHECK-NEXT: bb:
; CHECK-NEXT: [[T:%.*]] = getelementptr inbounds [0 x i32], <4 x ptr> <ptr @global, ptr poison, ptr poison, ptr poison>, <4 x i64> <i64 0, i64 poison, i64 poison, i64 poison>, <4 x i64> [[ARG:%.*]]
; CHECK-NEXT: [[T2:%.*]] = extractelement <4 x ptr> [[T]], i64 0
; CHECK-NEXT: [[TMP0:%.*]] = extractelement <4 x i64> [[ARG:%.*]], i64 0
; CHECK-NEXT: [[T2:%.*]] = getelementptr inbounds [0 x i32], ptr @global, i64 0, i64 [[TMP0]]
; CHECK-NEXT: ret ptr [[T2]]
;
bb:
Expand Down
24 changes: 9 additions & 15 deletions llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -528,9 +528,7 @@ define ptr @gep_splat_base_w_s_idx(ptr %base) {

define ptr @gep_splat_base_w_cv_idx(ptr %base) {
; CHECK-LABEL: @gep_splat_base_w_cv_idx(
; CHECK-NEXT: [[BASEVEC2:%.*]] = insertelement <2 x ptr> poison, ptr [[BASE:%.*]], i64 1
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, <2 x ptr> [[BASEVEC2]], <2 x i64> <i64 poison, i64 1>
; CHECK-NEXT: [[EE:%.*]] = extractelement <2 x ptr> [[GEP]], i64 1
; CHECK-NEXT: [[EE:%.*]] = getelementptr i8, ptr [[BASE:%.*]], i64 4
; CHECK-NEXT: ret ptr [[EE]]
;
%basevec1 = insertelement <2 x ptr> undef, ptr %base, i32 0
Expand All @@ -542,9 +540,8 @@ define ptr @gep_splat_base_w_cv_idx(ptr %base) {

define ptr @gep_splat_base_w_vidx(ptr %base, <2 x i64> %idxvec) {
; CHECK-LABEL: @gep_splat_base_w_vidx(
; CHECK-NEXT: [[BASEVEC2:%.*]] = insertelement <2 x ptr> poison, ptr [[BASE:%.*]], i64 1
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, <2 x ptr> [[BASEVEC2]], <2 x i64> [[IDXVEC:%.*]]
; CHECK-NEXT: [[EE:%.*]] = extractelement <2 x ptr> [[GEP]], i64 1
; CHECK-NEXT: [[TMP1:%.*]] = extractelement <2 x i64> [[IDXVEC:%.*]], i64 1
; CHECK-NEXT: [[EE:%.*]] = getelementptr i32, ptr [[BASE:%.*]], i64 [[TMP1]]
; CHECK-NEXT: ret ptr [[EE]]
;
%basevec1 = insertelement <2 x ptr> undef, ptr %base, i32 0
Expand Down Expand Up @@ -600,10 +597,7 @@ define ptr @gep_sbase_w_splat_idx(ptr %base, i64 %idx) {
}
define ptr @gep_splat_both(ptr %base, i64 %idx) {
; CHECK-LABEL: @gep_splat_both(
; CHECK-NEXT: [[BASEVEC2:%.*]] = insertelement <2 x ptr> poison, ptr [[BASE:%.*]], i64 1
; CHECK-NEXT: [[IDXVEC2:%.*]] = insertelement <2 x i64> poison, i64 [[IDX:%.*]], i64 1
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, <2 x ptr> [[BASEVEC2]], <2 x i64> [[IDXVEC2]]
; CHECK-NEXT: [[EE:%.*]] = extractelement <2 x ptr> [[GEP]], i64 1
; CHECK-NEXT: [[EE:%.*]] = getelementptr i32, ptr [[BASE:%.*]], i64 [[IDX:%.*]]
; CHECK-NEXT: ret ptr [[EE]]
;
%basevec1 = insertelement <2 x ptr> undef, ptr %base, i32 0
Expand Down Expand Up @@ -644,9 +638,9 @@ define ptr @gep_demanded_lane_undef(ptr %base, i64 %idx) {
;; indices.
define ptr @PR41624(<2 x ptr> %a) {
; CHECK-LABEL: @PR41624(
; CHECK-NEXT: [[W:%.*]] = getelementptr { i32, i32 }, <2 x ptr> [[A:%.*]], <2 x i64> splat (i64 5), <2 x i32> zeroinitializer
; CHECK-NEXT: [[R:%.*]] = extractelement <2 x ptr> [[W]], i64 0
; CHECK-NEXT: ret ptr [[R]]
; CHECK-NEXT: [[R:%.*]] = extractelement <2 x ptr> [[W:%.*]], i64 0
; CHECK-NEXT: [[R1:%.*]] = getelementptr i8, ptr [[R]], i64 40
; CHECK-NEXT: ret ptr [[R1]]
;
%w = getelementptr { i32, i32 }, <2 x ptr> %a, <2 x i64> <i64 5, i64 5>, <2 x i32> zeroinitializer
%r = extractelement <2 x ptr> %w, i32 0
Expand All @@ -660,8 +654,8 @@ define ptr @PR41624(<2 x ptr> %a) {
define ptr @zero_sized_type_extract(<4 x i64> %arg, i64 %arg1) {
; CHECK-LABEL: @zero_sized_type_extract(
; CHECK-NEXT: bb:
; CHECK-NEXT: [[T:%.*]] = getelementptr inbounds [0 x i32], <4 x ptr> <ptr @global, ptr poison, ptr poison, ptr poison>, <4 x i64> <i64 0, i64 poison, i64 poison, i64 poison>, <4 x i64> [[ARG:%.*]]
; CHECK-NEXT: [[T2:%.*]] = extractelement <4 x ptr> [[T]], i64 0
; CHECK-NEXT: [[TMP0:%.*]] = extractelement <4 x i64> [[ARG:%.*]], i64 0
; CHECK-NEXT: [[T2:%.*]] = getelementptr inbounds [0 x i32], ptr @global, i64 0, i64 [[TMP0]]
; CHECK-NEXT: ret ptr [[T2]]
;
bb:
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/vector_gep1-inseltpoison.ll
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Expand Up @@ -55,7 +55,7 @@ define <2 x i1> @test5(<2 x ptr> %a) {

define <2 x ptr> @test7(<2 x ptr> %a) {
; CHECK-LABEL: @test7(
; CHECK-NEXT: [[W:%.*]] = getelementptr { i32, i32 }, <2 x ptr> [[A:%.*]], <2 x i64> <i64 5, i64 9>, <2 x i32> zeroinitializer
; CHECK-NEXT: [[W:%.*]] = getelementptr { i32, i32 }, <2 x ptr> [[A:%.*]], <2 x i64> <i64 5, i64 9>, i32 0
; CHECK-NEXT: ret <2 x ptr> [[W]]
;
%w = getelementptr {i32, i32}, <2 x ptr> %a, <2 x i32> <i32 5, i32 9>, <2 x i32> zeroinitializer
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/vector_gep1.ll
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Expand Up @@ -55,7 +55,7 @@ define <2 x i1> @test5(<2 x ptr> %a) {

define <2 x ptr> @test7(<2 x ptr> %a) {
; CHECK-LABEL: @test7(
; CHECK-NEXT: [[W:%.*]] = getelementptr { i32, i32 }, <2 x ptr> [[A:%.*]], <2 x i64> <i64 5, i64 9>, <2 x i32> zeroinitializer
; CHECK-NEXT: [[W:%.*]] = getelementptr { i32, i32 }, <2 x ptr> [[A:%.*]], <2 x i64> <i64 5, i64 9>, i32 0
; CHECK-NEXT: ret <2 x ptr> [[W]]
;
%w = getelementptr {i32, i32}, <2 x ptr> %a, <2 x i32> <i32 5, i32 9>, <2 x i32> zeroinitializer
Expand Down
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