[ConstraintElim] Add facts for llvm.abs >= 0

[alexander-shaposhnikov]

Add facts for llvm.abs >= 0.

https://alive2.llvm.org/ce/z/GXnMHu

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Alexander Shaposhnikov (alexander-shaposhnikov)

Changes

Add facts for llvm.abs >= 0.

---

Full diff: https://github.com/llvm/llvm-project/pull/79070.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/ConstraintElimination.cpp (+4-1)
• (modified) llvm/test/Transforms/ConstraintElimination/abs.ll (+45)

diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 8f09569d0d9cc9f..6d0f57c1f6c8a41 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -1725,7 +1725,10 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
     if (!CB.isConditionFact()) {
       Value *X;
       if (match(CB.Inst, m_Intrinsic<Intrinsic::abs>(m_Value(X)))) {
-        // TODO: Add CB.Inst >= 0 fact.
+        // If is_int_min_poison is true then we may assume llvm.abs >= 0.
+        if (!cast<ConstantInt>(CB.Inst->getOperand(1))->isZero())
+          AddFact(CmpInst::ICMP_SGE, CB.Inst,
+                  ConstantInt::get(CB.Inst->getType(), 0));
         AddFact(CmpInst::ICMP_SGE, CB.Inst, X);
         continue;
       }
diff --git a/llvm/test/Transforms/ConstraintElimination/abs.ll b/llvm/test/Transforms/ConstraintElimination/abs.ll
index c3162ba48c2e4af..9fc68b0e72663fc 100644
--- a/llvm/test/Transforms/ConstraintElimination/abs.ll
+++ b/llvm/test/Transforms/ConstraintElimination/abs.ll
@@ -114,5 +114,50 @@ define i1 @abs_constant_positive_arg() {
   ret i1 %cmp
 }
 
+define i1 @abs_is_nonnegative_except_for_int_min_if_int_min_is_not_poison(i32 %arg) {
+; CHECK-LABEL: define i1 @abs_is_nonnegative_except_for_int_min_if_int_min_is_not_poison(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 false)
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge i32 [[ABS]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 false)
+  %cmp = icmp sge i32 %abs, 0
+  ret i1 %cmp
+}
+
+define i1 @abs_is_not_strictly_positive(i32 %arg) {
+; CHECK-LABEL: define i1 @abs_is_not_strictly_positive(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[ABS]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
+  %cmp = icmp sgt i32 %abs, 0
+  ret i1 %cmp
+}
+
+define i1 @abs_is_nonnegative_int_min_is_poison(i32 %arg) {
+; CHECK-LABEL: define i1 @abs_is_nonnegative_int_min_is_poison(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
+; CHECK-NEXT:    ret i1 true
+;
+  %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
+  %cmp = icmp sge i32 %abs, 0
+  ret i1 %cmp
+}
+
+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)
+  %cmp = icmp sge i32 %abs, 0
+  ret i1 %cmp
+}
+
 declare i32 @llvm.abs.i32(i32, i1 immarg)
 declare void @llvm.assume(i1)

[alexander-shaposhnikov]

@fhahn - I've just rebased the patch

[alexander-shaposhnikov]

gentle ping @fhahn

[alexander-shaposhnikov]

@fhahn - what would you say to submitting this ?

(tests for this change: #79068)

[nikic]

LGTM