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[ConstraintElim] Opimize abs based on known constraints #135754

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[ConstraintElim] Opimize abs based on known constraints #135754

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49fa9b3
[ConstraintElim] Opimize abs based on known constraints
el-ev Apr 15, 2025
7484739
update test
el-ev Apr 15, 2025
5127b51
match abs only
el-ev Apr 15, 2025
157aa8a
add nopoison back
el-ev Apr 15, 2025
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28 changes: 26 additions & 2 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1128,18 +1128,17 @@ void State::addInfoFor(BasicBlock &BB) {
FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
break;
// Enqueue the intrinsics to add extra info.
case Intrinsic::abs:
case Intrinsic::umin:
case Intrinsic::umax:
case Intrinsic::smin:
case Intrinsic::smax:
case Intrinsic::usub_sat:
// TODO: handle llvm.abs as well
WorkList.push_back(
FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
// TODO: Check if it is possible to instead only added the min/max facts
// when simplifying uses of the min/max intrinsics.
[[fallthrough]];
case Intrinsic::abs:
case Intrinsic::uadd_sat:
if (!isGuaranteedNotToBePoison(&I))
break;
Expand Down Expand Up @@ -1537,6 +1536,28 @@ static bool checkAndReplaceUSubSat(SaturatingInst *I, ConstraintInfo &Info,
return false;
}

static bool checkAndReplaceAbs(IntrinsicInst *I, ConstraintInfo &Info,
SmallVectorImpl<Instruction *> &ToRemove) {
assert(I->getIntrinsicID() == Intrinsic::abs && "Expected abs intrinsic");
Value *Op = I->getOperand(0);
if (checkCondition(ICmpInst::ICMP_SGE, Op, ConstantInt::get(Op->getType(), 0),
I, Info)
.value_or(false)) {
I->replaceAllUsesWith(Op);
ToRemove.push_back(I);
return true;
}
if (checkCondition(ICmpInst::ICMP_SLT, Op, ConstantInt::get(Op->getType(), 0),
I, Info)
.value_or(false)) {
IRBuilder<> Builder(I->getParent(), I->getIterator());
I->replaceAllUsesWith(Builder.CreateNeg(Op));
ToRemove.push_back(I);
return true;
}
return false;
}

static void
removeEntryFromStack(const StackEntry &E, ConstraintInfo &Info,
Module *ReproducerModule,
Expand Down Expand Up @@ -1858,6 +1879,9 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
Changed |= checkAndReplaceMinMax(MinMax, Info, ToRemove);
} else if (auto *CmpIntr = dyn_cast<CmpIntrinsic>(Inst)) {
Changed |= checkAndReplaceCmp(CmpIntr, Info, ToRemove);
} else if (match(Inst, m_Intrinsic<Intrinsic::abs>(m_Value()))) {
Changed |=
checkAndReplaceAbs(dyn_cast<IntrinsicInst>(Inst), Info, ToRemove);
} else if (auto *SatIntr = dyn_cast<SaturatingInst>(Inst)) {
if (SatIntr->getIntrinsicID() == Intrinsic::usub_sat)
Changed |= checkAndReplaceUSubSat(SatIntr, Info, ToRemove);
Expand Down
57 changes: 46 additions & 11 deletions llvm/test/Transforms/ConstraintElimination/abs.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -72,10 +72,8 @@ define i1 @abs_plus_one_unsigned_greater_or_equal_nonnegative_arg(i32 %arg) {
; CHECK-SAME: i32 [[ARG:%.*]]) {
; CHECK-NEXT: [[CMP_ARG_NONNEGATIVE:%.*]] = icmp sge i32 [[ARG]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP_ARG_NONNEGATIVE]])
; CHECK-NEXT: [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
; CHECK-NEXT: [[ABS_PLUS_ONE:%.*]] = add nuw i32 [[ABS]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp uge i32 [[ABS_PLUS_ONE]], [[ARG]]
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: [[ABS_PLUS_ONE:%.*]] = add nuw i32 [[ARG]], 1
; CHECK-NEXT: ret i1 true
;
%cmp_arg_nonnegative = icmp sge i32 %arg, 0
call void @llvm.assume(i1 %cmp_arg_nonnegative)
Expand All @@ -101,9 +99,7 @@ define i1 @abs_plus_one_unsigned_greater_or_equal_cannot_be_simplified(i32 %arg)

define i1 @abs_constant_negative_arg() {
; CHECK-LABEL: define i1 @abs_constant_negative_arg() {
; CHECK-NEXT: [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 -3, i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp sge i32 [[ABS]], 3
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
;
%abs = tail call i32 @llvm.abs.i32(i32 -3, i1 false)
%cmp = icmp sge i32 %abs, 3
Expand All @@ -112,7 +108,6 @@ define i1 @abs_constant_negative_arg() {

define i1 @abs_constant_positive_arg() {
; CHECK-LABEL: define i1 @abs_constant_positive_arg() {
; CHECK-NEXT: [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 3, i1 false)
; CHECK-NEXT: ret i1 true
;
%abs = tail call i32 @llvm.abs.i32(i32 3, i1 false)
Expand Down Expand Up @@ -158,14 +153,54 @@ define i1 @abs_is_nonnegative_int_min_is_poison(i32 %arg) {

define i1 @abs_is_nonnegative_constant_arg() {
; CHECK-LABEL: define i1 @abs_is_nonnegative_constant_arg() {
; CHECK-NEXT: [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 -3, i1 true)
; CHECK-NEXT: [[CMP:%.*]] = icmp sge i32 [[ABS]], 0
; CHECK-NEXT: ret i1 [[CMP]]
; CHECK-NEXT: ret i1 true
;
%abs = tail call i32 @llvm.abs.i32(i32 -3, i1 true)
%cmp = icmp sge i32 %abs, 0
ret i1 %cmp
}

define i64 @abs_assume_nonnegative(i64 %arg) {
; CHECK-LABEL: define i64 @abs_assume_nonnegative(
; CHECK-SAME: i64 [[ARG:%.*]]) {
; CHECK-NEXT: [[PRECOND:%.*]] = icmp sge i64 [[ARG]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[PRECOND]])
; CHECK-NEXT: ret i64 [[ARG]]
;
%precond = icmp sge i64 %arg, 0
call void @llvm.assume(i1 %precond)
%abs = tail call i64 @llvm.abs.i64(i64 %arg, i1 false)
ret i64 %abs
}

define i64 @abs_assume_negative(i64 %arg) {
; CHECK-LABEL: define i64 @abs_assume_negative(
; CHECK-SAME: i64 [[ARG:%.*]]) {
; CHECK-NEXT: [[PRECOND:%.*]] = icmp slt i64 [[ARG]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[PRECOND]])
; CHECK-NEXT: [[ABS:%.*]] = sub i64 0, [[ARG]]
; CHECK-NEXT: ret i64 [[ABS]]
;
%precond = icmp slt i64 %arg, 0
call void @llvm.assume(i1 %precond)
%abs = tail call i64 @llvm.abs.i64(i64 %arg, i1 false)
ret i64 %abs
}

; Negative test
define i64 @abs_assume_unrelated(i64 %arg) {
; CHECK-LABEL: define i64 @abs_assume_unrelated(
; CHECK-SAME: i64 [[ARG:%.*]]) {
; CHECK-NEXT: [[PRECOND:%.*]] = icmp slt i64 [[ARG]], 3
; CHECK-NEXT: call void @llvm.assume(i1 [[PRECOND]])
; CHECK-NEXT: [[ABS:%.*]] = tail call i64 @llvm.abs.i64(i64 [[ARG]], i1 false)
; CHECK-NEXT: ret i64 [[ABS]]
;
%precond = icmp slt i64 %arg, 3
call void @llvm.assume(i1 %precond)
%abs = tail call i64 @llvm.abs.i64(i64 %arg, i1 false)
ret i64 %abs
}

declare i32 @llvm.abs.i32(i32, i1 immarg)
declare void @llvm.assume(i1)
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