[ConstantRange] Sign-flipping of signedness-invariant comparisons

For certain combination of LHS and RHS constant ranges,
the signedness of the relational comparison predicate is irrelevant.

This implements complete and precise model for all predicates,
as confirmed by the brute-force tests. I'm not sure if there are
some more cases that we can handle here.

In a follow-up, CVP will make use of this.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D90924

1 files changed, 36 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index a37790d..d37c969 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -147,6 +147,42 @@ ConstantRange ConstantRange::makeExactICmpRegion(CmpInst::Predicate Pred,
   return makeAllowedICmpRegion(Pred, C);
 }
 
+bool ConstantRange::areInsensitiveToSignednessOfICmpPredicate(
+    const ConstantRange &CR1, const ConstantRange &CR2) {
+  if (CR1.isEmptySet() || CR2.isEmptySet())
+    return true;
+
+  return (CR1.isAllNonNegative() && CR2.isAllNonNegative()) ||
+         (CR1.isAllNegative() && CR2.isAllNegative());
+}
+
+bool ConstantRange::areInsensitiveToSignednessOfInvertedICmpPredicate(
+    const ConstantRange &CR1, const ConstantRange &CR2) {
+  if (CR1.isEmptySet() || CR2.isEmptySet())
+    return true;
+
+  return (CR1.isAllNonNegative() && CR2.isAllNegative()) ||
+         (CR1.isAllNegative() && CR2.isAllNonNegative());
+}
+
+CmpInst::Predicate ConstantRange::getEquivalentPredWithFlippedSignedness(
+    CmpInst::Predicate Pred, const ConstantRange &CR1,
+    const ConstantRange &CR2) {
+  assert(CmpInst::isIntPredicate(Pred) && CmpInst::isRelational(Pred) &&
+         "Only for relational integer predicates!");
+
+  CmpInst::Predicate FlippedSignednessPred =
+      CmpInst::getFlippedSignednessPredicate(Pred);
+
+  if (areInsensitiveToSignednessOfICmpPredicate(CR1, CR2))
+    return FlippedSignednessPred;
+
+  if (areInsensitiveToSignednessOfInvertedICmpPredicate(CR1, CR2))
+    return CmpInst::getInversePredicate(FlippedSignednessPred);
+
+  return CmpInst::Predicate::BAD_ICMP_PREDICATE;
+}
+
 bool ConstantRange::getEquivalentICmp(CmpInst::Predicate &Pred,
                                       APInt &RHS) const {
   bool Success = false;