[ConstraintElim] Opimize abs based on known constraints

[el-ev]

[ConstraintElim] Opimize abs based on known constraints

update test

[el-ev]

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• [ConstraintElim] Add noundef to several testcases (NFC) #135799
• [ConstraintElim] Opimize abs based on known constraints #135754 👈 (View in Graphite)
• [ConstraintElim] Optimize usub.sat intrinsic based on known constraints #135744
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✅ With the latest revision this PR passed the C/C++ code formatter.

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@llvm/pr-subscribers-llvm-transforms

Author: Iris (el-ev)

Changes

[ConstraintElim] Opimize abs based on known constraints

update test

---

Full diff: https://github.com/llvm/llvm-project/pull/135754.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/ConstraintElimination.cpp (+27-2)
• (modified) llvm/test/Transforms/ConstraintElimination/abs.ll (+44-7)

diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 6608d65f797c5..9eedd701b5e00 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)));
       [[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..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)
@@ -159,5 +154,47 @@ 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:    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)