https://github.com/el-ev created
https://github.com/llvm/llvm-project/pull/135754
[ConstraintElim] Opimize abs based on known constraints
update test
>From af8e5662259fe323f403a48140443feb22e9ef63 Mon Sep 17 00:00:00 2001
From: Iris Shi <0...@owo.li>
Date: Tue, 15 Apr 2025 15:00:58 +0800
Subject: [PATCH 1/2] [ConstraintElim] Opimize abs based on known constraints
---
.../Scalar/ConstraintElimination.cpp | 31 +++++++++++--
.../Transforms/ConstraintElimination/abs.ll | 43 +++++++++++++++++++
2 files changed, 71 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 6608d65f797c5..dca55cc48d91f 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -1132,7 +1132,6 @@ void State::addInfoFor(BasicBlock &BB) {
case Intrinsic::umax:
case Intrinsic::smin:
case Intrinsic::smax:
- // 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
@@ -1140,11 +1139,11 @@ void State::addInfoFor(BasicBlock &BB) {
if (isGuaranteedNotToBePoison(&I))
WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
break;
+ case Intrinsic::abs:
case Intrinsic::usub_sat:
WorkList.push_back(
- FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
+ FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
[[fallthrough]];
- case Intrinsic::abs:
case Intrinsic::uadd_sat:
WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
break;
@@ -1540,6 +1539,28 @@ 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,
@@ -1866,6 +1887,10 @@ static bool eliminateConstraints(Function &F,
DominatorTree &DT, LoopInfo &LI,
Changed |= checkAndReplaceUSubSat(SatIntr, Info, ToRemove);
else
llvm_unreachable("Unexpected intrinsic.");
+ } else if (auto *II = dyn_cast<IntrinsicInst>(Inst)) {
+ if (II->getIntrinsicID() == Intrinsic::abs) {
+ Changed |= checkAndReplaceAbs(II, Info, ToRemove);
+ }
}
continue;
}
diff --git a/llvm/test/Transforms/ConstraintElimination/abs.ll
b/llvm/test/Transforms/ConstraintElimination/abs.ll
index 9fc68b0e72663..32f686a6fcb8f 100644
--- a/llvm/test/Transforms/ConstraintElimination/abs.ll
+++ b/llvm/test/Transforms/ConstraintElimination/abs.ll
@@ -159,5 +159,48 @@ define i1 @abs_is_nonnegative_constant_arg() {
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: [[ABS:%.*]] = tail call i64 @llvm.abs.i64(i64 [[ARG]], i1
false)
+; CHECK-NEXT: ret i64 [[ABS]]
+;
+ %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:%.*]] = tail call i64 @llvm.abs.i64(i64 [[ARG]], i1
false)
+; 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)
>From e43776bf35377832829b53a959c377276b37c327 Mon Sep 17 00:00:00 2001
From: Iris Shi <0...@owo.li>
Date: Tue, 15 Apr 2025 15:03:08 +0800
Subject: [PATCH 2/2] update test
---
llvm/test/Transforms/ConstraintElimination/abs.ll | 14 ++++----------
1 file changed, 4 insertions(+), 10 deletions(-)
diff --git a/llvm/test/Transforms/ConstraintElimination/abs.ll
b/llvm/test/Transforms/ConstraintElimination/abs.ll
index 32f686a6fcb8f..e09a061410f48 100644
--- a/llvm/test/Transforms/ConstraintElimination/abs.ll
+++ b/llvm/test/Transforms/ConstraintElimination/abs.ll
@@ -67,8 +67,7 @@ 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: [[ABS_PLUS_ONE:%.*]] = add nuw i32 [[ARG]], 1
; CHECK-NEXT: ret i1 true
;
%cmp_arg_nonnegative = icmp sge i32 %arg, 0
@@ -95,9 +94,7 @@ 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
@@ -106,7 +103,6 @@ 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)
@@ -151,7 +147,6 @@ 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: ret i1 true
;
%abs = tail call i32 @llvm.abs.i32(i32 -3, i1 true)
@@ -164,8 +159,7 @@ define i64 @abs_assume_nonnegative(i64 %arg) {
; CHECK-SAME: i64 [[ARG:%.*]]) {
; CHECK-NEXT: [[PRECOND:%.*]] = icmp sge i64 [[ARG]], 0
; 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]]
+; CHECK-NEXT: ret i64 [[ARG]]
;
%precond = icmp sge i64 %arg, 0
call void @llvm.assume(i1 %precond)
@@ -178,7 +172,7 @@ define i64 @abs_assume_negative(i64 %arg) {
; CHECK-SAME: i64 [[ARG:%.*]]) {
; CHECK-NEXT: [[PRECOND:%.*]] = icmp slt i64 [[ARG]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[PRECOND]])
-; CHECK-NEXT: [[ABS:%.*]] = tail call i64 @llvm.abs.i64(i64 [[ARG]], i1
false)
+; CHECK-NEXT: [[ABS:%.*]] = sub i64 0, [[ARG]]
; CHECK-NEXT: ret i64 [[ABS]]
;
%precond = icmp slt i64 %arg, 0
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