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[InstCombine] Fold icmp over select of cmp more aggressively #105536

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Aug 22, 2024
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[InstCombine] Fold icmp over select of cmp more aggressively #105536

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6c3ecf6
[InstCombine] Fold icmp over select of cmp more aggressively
nikic Aug 21, 2024
d88b599
Only allow splat constants
nikic Aug 21, 2024
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10 changes: 9 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4209,6 +4209,14 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
if (Op2)
CI = dyn_cast<ConstantInt>(Op2);

auto Simplifies = [&](Value *Op, unsigned Idx) {
// A comparison of ucmp/scmp with a constant will fold into an icmp.
const APInt *Dummy;
return Op ||
(isa<CmpIntrinsic>(SI->getOperand(Idx)) &&
SI->getOperand(Idx)->hasOneUse() && match(RHS, m_APInt(Dummy)));
};

// We only want to perform this transformation if it will not lead to
// additional code. This is true if either both sides of the select
// fold to a constant (in which case the icmp is replaced with a select
Expand All @@ -4219,7 +4227,7 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
bool Transform = false;
if (Op1 && Op2)
Transform = true;
else if (Op1 || Op2) {
else if (Simplifies(Op1, 1) || Simplifies(Op2, 2)) {
// Local case
if (SI->hasOneUse())
Transform = true;
Expand Down
54 changes: 41 additions & 13 deletions llvm/test/Transforms/InstCombine/select-cmp.ll
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Expand Up @@ -482,10 +482,9 @@ define i1 @test_select_inverse_nonconst4(i64 %x, i64 %y, i64 %z, i1 %cond) {

define i1 @sel_icmp_two_cmp(i1 %c, i32 %a1, i32 %a2, i32 %a3, i32 %a4) {
; CHECK-LABEL: @sel_icmp_two_cmp(
; CHECK-NEXT: [[V1:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A1:%.*]], i32 [[A2:%.*]])
; CHECK-NEXT: [[V2:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A3:%.*]], i32 [[A4:%.*]])
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[C:%.*]], i8 [[V1]], i8 [[V2]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[SEL]], 1
; CHECK-NEXT: [[CMP1:%.*]] = icmp ule i32 [[A1:%.*]], [[A2:%.*]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp sle i32 [[A3:%.*]], [[A4:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = select i1 [[C:%.*]], i1 [[CMP1]], i1 [[CMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%v1 = call i8 @llvm.ucmp(i32 %a1, i32 %a2)
Expand All @@ -498,10 +497,10 @@ define i1 @sel_icmp_two_cmp(i1 %c, i32 %a1, i32 %a2, i32 %a3, i32 %a4) {
define i1 @sel_icmp_two_cmp_extra_use1(i1 %c, i32 %a1, i32 %a2, i32 %a3, i32 %a4) {
; CHECK-LABEL: @sel_icmp_two_cmp_extra_use1(
; CHECK-NEXT: [[V1:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A1:%.*]], i32 [[A2:%.*]])
; CHECK-NEXT: [[V2:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A3:%.*]], i32 [[A4:%.*]])
; CHECK-NEXT: call void @use.i8(i8 [[V1]])
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[C:%.*]], i8 [[V1]], i8 [[V2]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[SEL]], 1
; CHECK-NEXT: [[CMP1:%.*]] = icmp ule i32 [[A1]], [[A2]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp sle i32 [[A3:%.*]], [[A4:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = select i1 [[C:%.*]], i1 [[CMP1]], i1 [[CMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%v1 = call i8 @llvm.ucmp(i32 %a1, i32 %a2)
Expand Down Expand Up @@ -544,6 +543,35 @@ define i1 @sel_icmp_two_cmp_not_const(i1 %c, i32 %a1, i32 %a2, i32 %a3, i32 %a4,
ret i1 %cmp
}

define <2 x i1> @sel_icmp_two_cmp_vec(i1 %c, <2 x i32> %a1, <2 x i32> %a2, <2 x i32> %a3, <2 x i32> %a4) {
; CHECK-LABEL: @sel_icmp_two_cmp_vec(
; CHECK-NEXT: [[CMP1:%.*]] = icmp ule <2 x i32> [[A1:%.*]], [[A2:%.*]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp sle <2 x i32> [[A3:%.*]], [[A4:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = select i1 [[C:%.*]], <2 x i1> [[CMP1]], <2 x i1> [[CMP2]]
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%v1 = call <2 x i8> @llvm.ucmp(<2 x i32> %a1, <2 x i32> %a2)
%v2 = call <2 x i8> @llvm.scmp(<2 x i32> %a3, <2 x i32> %a4)
%sel = select i1 %c, <2 x i8> %v1, <2 x i8> %v2
%cmp = icmp sle <2 x i8> %sel, zeroinitializer
ret <2 x i1> %cmp
}

define <2 x i1> @sel_icmp_two_cmp_vec_nonsplat(i1 %c, <2 x i32> %a1, <2 x i32> %a2, <2 x i32> %a3, <2 x i32> %a4) {
; CHECK-LABEL: @sel_icmp_two_cmp_vec_nonsplat(
; CHECK-NEXT: [[V1:%.*]] = call <2 x i8> @llvm.ucmp.v2i8.v2i32(<2 x i32> [[A1:%.*]], <2 x i32> [[A2:%.*]])
; CHECK-NEXT: [[V2:%.*]] = call <2 x i8> @llvm.scmp.v2i8.v2i32(<2 x i32> [[A3:%.*]], <2 x i32> [[A4:%.*]])
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[C:%.*]], <2 x i8> [[V1]], <2 x i8> [[V2]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt <2 x i8> [[SEL]], <i8 1, i8 2>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%v1 = call <2 x i8> @llvm.ucmp(<2 x i32> %a1, <2 x i32> %a2)
%v2 = call <2 x i8> @llvm.scmp(<2 x i32> %a3, <2 x i32> %a4)
%sel = select i1 %c, <2 x i8> %v1, <2 x i8> %v2
%cmp = icmp sle <2 x i8> %sel, <i8 0, i8 1>
ret <2 x i1> %cmp
}

define i1 @sel_icmp_cmp_and_simplify(i1 %c, i32 %a1, i32 %a2) {
; CHECK-LABEL: @sel_icmp_cmp_and_simplify(
; CHECK-NEXT: [[CMP1:%.*]] = icmp ule i32 [[A1:%.*]], [[A2:%.*]]
Expand All @@ -559,9 +587,9 @@ define i1 @sel_icmp_cmp_and_simplify(i1 %c, i32 %a1, i32 %a2) {

define i1 @sel_icmp_cmp_and_no_simplify(i1 %c, i32 %a1, i32 %a2, i8 %b) {
; CHECK-LABEL: @sel_icmp_cmp_and_no_simplify(
; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A1:%.*]], i32 [[A2:%.*]])
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[C:%.*]], i8 [[V]], i8 [[B:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[SEL]], 1
; CHECK-NEXT: [[CMP1:%.*]] = icmp ule i32 [[A1:%.*]], [[A2:%.*]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[B:%.*]], 1
; CHECK-NEXT: [[CMP:%.*]] = select i1 [[C:%.*]], i1 [[CMP1]], i1 [[CMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%v = call i8 @llvm.ucmp(i32 %a1, i32 %a2)
Expand All @@ -572,9 +600,9 @@ define i1 @sel_icmp_cmp_and_no_simplify(i1 %c, i32 %a1, i32 %a2, i8 %b) {

define i1 @sel_icmp_cmp_and_no_simplify_comm(i1 %c, i32 %a1, i32 %a2, i8 %b) {
; CHECK-LABEL: @sel_icmp_cmp_and_no_simplify_comm(
; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A1:%.*]], i32 [[A2:%.*]])
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[C:%.*]], i8 [[B:%.*]], i8 [[V]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[SEL]], 1
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[B:%.*]], 1
; CHECK-NEXT: [[CMP2:%.*]] = icmp ule i32 [[A1:%.*]], [[A2:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = select i1 [[C:%.*]], i1 [[CMP1]], i1 [[CMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%v = call i8 @llvm.ucmp(i32 %a1, i32 %a2)
Expand Down
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