Skip to content

[InstCombine] Preserve NSW/NUW flags when folding const BOp with min/max #143471

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 4 commits into from
Jun 13, 2025
Merged

[InstCombine] Preserve NSW/NUW flags when folding const BOp with min/max #143471

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
6bee710
pre-commit tests
AlexMaclean Jun 9, 2025
16bc374
[InstCombine] Preserve NSW/NUW flags when folding const BOp with min/max
AlexMaclean Jun 9, 2025
8d6be44
Update llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
AlexMaclean Jun 10, 2025
7940b46
Update llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
AlexMaclean Jun 10, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 2 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineInternal.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -767,6 +767,8 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
Value *A, Value *B, Instruction &Outer,
SelectPatternFlavor SPF2, Value *C);
Instruction *foldSelectInstWithICmp(SelectInst &SI, ICmpInst *ICI);
Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,
Value *FalseVal);
Instruction *foldSelectValueEquivalence(SelectInst &SI, CmpInst &CI);
bool replaceInInstruction(Value *V, Value *Old, Value *New,
unsigned Depth = 0);
Expand Down
36 changes: 27 additions & 9 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1823,9 +1823,9 @@ static Instruction *foldSelectICmpEq(SelectInst &SI, ICmpInst *ICI,

/// Fold `X Pred C1 ? X BOp C2 : C1 BOp C2` to `min/max(X, C1) BOp C2`.
/// This allows for better canonicalization.
static Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,
Value *FalseVal,
IRBuilderBase &Builder) {
Value *InstCombinerImpl::foldSelectWithConstOpToBinOp(ICmpInst *Cmp,
Value *TrueVal,
Value *FalseVal) {
Constant *C1, *C2, *C3;
Value *X;
CmpPredicate Predicate;
Expand Down Expand Up @@ -1889,11 +1889,29 @@ static Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,
return nullptr;
}

Intrinsic::ID IntrinsicID = getMinMaxIntrinsic(SPF);
Value *Intrinsic = Builder.CreateBinaryIntrinsic(IntrinsicID, X, RHS);
return IsIntrinsic ? Builder.CreateBinaryIntrinsic(Opcode, Intrinsic, C2)
: Builder.CreateBinOp(Instruction::BinaryOps(Opcode),
Intrinsic, C2);
Intrinsic::ID MinMaxID = getMinMaxIntrinsic(SPF);
Value *MinMax = Builder.CreateBinaryIntrinsic(MinMaxID, X, RHS);
if (IsIntrinsic)
return Builder.CreateBinaryIntrinsic(Opcode, MinMax, C2);

const auto BinOpc = Instruction::BinaryOps(Opcode);
Value *BinOp = Builder.CreateBinOp(BinOpc, MinMax, C2);

// If we can attach no-wrap flags to the new instruction, do so if the
// old instruction had them and C1 BinOp C2 does not overflow.
if (Instruction *BinOpInst = dyn_cast<Instruction>(BinOp)) {
if (BinOpc == Instruction::Add || BinOpc == Instruction::Sub ||
BinOpc == Instruction::Mul) {
Instruction *OldBinOp = cast<BinaryOperator>(TrueVal);
if (OldBinOp->hasNoSignedWrap() &&
willNotOverflow(BinOpc, RHS, C2, *BinOpInst, /*IsSigned=*/true))
BinOpInst->setHasNoSignedWrap();
if (OldBinOp->hasNoUnsignedWrap() &&
willNotOverflow(BinOpc, RHS, C2, *BinOpInst, /*IsSigned=*/false))
BinOpInst->setHasNoUnsignedWrap();
}
}
return BinOp;
}

/// Visit a SelectInst that has an ICmpInst as its first operand.
Expand Down Expand Up @@ -1968,7 +1986,7 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
if (Value *V = foldAbsDiff(ICI, TrueVal, FalseVal, Builder))
return replaceInstUsesWith(SI, V);

if (Value *V = foldSelectWithConstOpToBinOp(ICI, TrueVal, FalseVal, Builder))
if (Value *V = foldSelectWithConstOpToBinOp(ICI, TrueVal, FalseVal))
return replaceInstUsesWith(SI, V);

return Changed ? &SI : nullptr;
Expand Down
83 changes: 81 additions & 2 deletions llvm/test/Transforms/InstCombine/canonicalize-const-to-bop.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ define i8 @add_and_sgt(i8 %x) {
; CHECK-LABEL: define i8 @add_and_sgt(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smax.i8(i8 [[X]], i8 8)
; CHECK-NEXT: [[S:%.*]] = add nuw i8 [[TMP1]], 16
; CHECK-NEXT: [[S:%.*]] = add nuw nsw i8 [[TMP1]], 16
; CHECK-NEXT: ret i8 [[S]]
;
%add = add nsw i8 %x, 16
Expand Down Expand Up @@ -155,7 +155,7 @@ define i8 @multi_use_cond_and_sel(i8 %x) {
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[X]], 8
; CHECK-NEXT: call void @use(i1 [[CMP]])
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smax.i8(i8 [[X]], i8 8)
; CHECK-NEXT: [[S:%.*]] = add nuw i8 [[TMP1]], 16
; CHECK-NEXT: [[S:%.*]] = add nuw nsw i8 [[TMP1]], 16
; CHECK-NEXT: call void @use_byte(i8 [[S]])
; CHECK-NEXT: ret i8 [[S]]
;
Expand Down Expand Up @@ -450,3 +450,82 @@ define i8 @umax_sgt(i8 %x) {
%s = select i1 %cmp, i8 100, i8 %umax
ret i8 %s
}

define i8 @add_sgt_nuw_nsw_safe(i8 %x) {
; CHECK-LABEL: define i8 @add_sgt_nuw_nsw_safe(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X]], i8 100)
; CHECK-NEXT: [[S:%.*]] = add nuw nsw i8 [[TMP1]], 1
; CHECK-NEXT: ret i8 [[S]]
;
%add = add nuw nsw i8 %x, 1
%cmp = icmp sgt i8 %x, 100
%s = select i1 %cmp, i8 101, i8 %add
ret i8 %s
}

define i8 @add_sgt_nuw_only(i8 %x) {
; CHECK-LABEL: define i8 @add_sgt_nuw_only(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X]], i8 100)
; CHECK-NEXT: [[S:%.*]] = add nuw i8 [[TMP1]], 50
; CHECK-NEXT: ret i8 [[S]]
;
%add = add nuw nsw i8 %x, 50
%cmp = icmp sgt i8 %x, 100
%s = select i1 %cmp, i8 150, i8 %add
ret i8 %s
}

define i8 @add_sgt_nsw_only(i8 %x) {
; CHECK-LABEL: define i8 @add_sgt_nsw_only(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X]], i8 100)
; CHECK-NEXT: [[S:%.*]] = add nsw i8 [[TMP1]], -99
; CHECK-NEXT: ret i8 [[S]]
;
%add = add nuw nsw i8 %x, -99
%cmp = icmp sgt i8 %x, 100
%s = select i1 %cmp, i8 1, i8 %add
ret i8 %s
}


define i8 @mul_ult_nuw_nsw_safe(i8 %x) {
; CHECK-LABEL: define i8 @mul_ult_nuw_nsw_safe(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.umax.i8(i8 [[X]], i8 10)
; CHECK-NEXT: [[S:%.*]] = mul nuw nsw i8 [[TMP1]], 3
; CHECK-NEXT: ret i8 [[S]]
;
%mul = mul nuw nsw i8 %x, 3
%cmp = icmp ult i8 %x, 10
%s = select i1 %cmp, i8 30, i8 %mul
ret i8 %s
}

define i8 @mul_ult_nuw_only(i8 %x) {
; CHECK-LABEL: define i8 @mul_ult_nuw_only(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.umax.i8(i8 [[X]], i8 10)
; CHECK-NEXT: [[S:%.*]] = mul nuw i8 [[TMP1]], 25
; CHECK-NEXT: ret i8 [[S]]
;
%mul = mul nuw nsw i8 %x, 25
%cmp = icmp ult i8 %x, 10
%s = select i1 %cmp, i8 250, i8 %mul
ret i8 %s
}

define i8 @mul_ult_nsw_only(i8 %x) {
; CHECK-LABEL: define i8 @mul_ult_nsw_only(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.umax.i8(i8 [[X]], i8 40)
; CHECK-NEXT: [[S:%.*]] = mul nsw i8 [[TMP1]], -2
; CHECK-NEXT: ret i8 [[S]]
;
%mul = mul nuw nsw i8 %x, -2
%cmp = icmp ult i8 %x, 40
%s = select i1 %cmp, i8 -80, i8 %mul
ret i8 %s
}