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[InstCombine] Canonicalize uadd.with.overflow to uadd.sat 

This adds some patterns to transform uadd.with.overflow to uadd.sat
(with usub.with.overflow to usub.sat too). The patterns selects from
UINTMAX (or 0 for subs) depending on whether the operation overflowed.

Signed patterns are a little more involved (they can wrap in two
directions), but can be added here in a followup patch too.

Differential Revision: https://reviews.llvm.org/D69245
This commit is contained in:
David Green 2019-10-31 12:42:36 +00:00
parent a8db456b53
commit a5f7bc0de7
2 changed files with 34 additions and 8 deletions
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32
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -1732,6 +1732,36 @@ static Instruction *foldAddSubSelect(SelectInst &SI,
return nullptr;
}
/// Turn X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
/// And X - Y overflows ? 0 : X - Y -> usub_sat X, Y
static Instruction *
foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
WithOverflowInst *II;
if (!match(CondVal, m_ExtractValue<1>(m_WithOverflowInst(II))) ||
!match(FalseVal, m_ExtractValue<0>(m_Specific(II))))
return nullptr;
Intrinsic::ID NewIntrinsicID;
if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow &&
match(TrueVal, m_AllOnes()))
// X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
NewIntrinsicID = Intrinsic::uadd_sat;
else if (II->getIntrinsicID() == Intrinsic::usub_with_overflow &&
match(TrueVal, m_Zero()))
// X - Y overflows ? 0 : X - Y -> usub_sat X, Y
NewIntrinsicID = Intrinsic::usub_sat;
else
return nullptr;
Function *F =
Intrinsic::getDeclaration(SI.getModule(), NewIntrinsicID, SI.getType());
return CallInst::Create(F, {II->getArgOperand(0), II->getArgOperand(1)});
}
Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
Constant *C;
if (!match(Sel.getTrueValue(), m_Constant(C)) &&
@ -2398,6 +2428,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
if (Instruction *Add = foldAddSubSelect(SI, Builder))
return Add;
if (Instruction *Add = foldOverflowingAddSubSelect(SI, Builder))
return Add;
// Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
auto *TI = dyn_cast<Instruction>(TrueVal);

10
llvm/test/Transforms/InstCombine/overflow_to_sat.ll
View File

@ -3,10 +3,7 @@
define i32 @uadd(i32 %x, i32 %y) {
; CHECK-LABEL: @uadd(
; CHECK-NEXT: [[AO:%.*]] = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
; CHECK-NEXT: [[O:%.*]] = extractvalue { i32, i1 } [[AO]], 1
; CHECK-NEXT: [[A:%.*]] = extractvalue { i32, i1 } [[AO]], 0
; CHECK-NEXT: [[S:%.*]] = select i1 [[O]], i32 -1, i32 [[A]]
; CHECK-NEXT: [[S:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
; CHECK-NEXT: ret i32 [[S]]
;
%ao = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %x, i32 %y)
@ -18,10 +15,7 @@ define i32 @uadd(i32 %x, i32 %y) {
define i32 @usub(i32 %x, i32 %y) {
; CHECK-LABEL: @usub(
; CHECK-NEXT: [[AO:%.*]] = tail call { i32, i1 } @llvm.usub.with.overflow.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
; CHECK-NEXT: [[O:%.*]] = extractvalue { i32, i1 } [[AO]], 1
; CHECK-NEXT: [[A:%.*]] = extractvalue { i32, i1 } [[AO]], 0
; CHECK-NEXT: [[S:%.*]] = select i1 [[O]], i32 0, i32 [[A]]
; CHECK-NEXT: [[S:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
; CHECK-NEXT: ret i32 [[S]]
;
%ao = tail call { i32, i1 } @llvm.usub.with.overflow.i32(i32 %x, i32 %y)