[ConstantRange] Fix nsw nowrap region for 1 bit integers (PR59301)

The special case for V=1 was incorrect for one bit types, where
1 is also -1. Remove it, and use getNonEmpty() to handle the full
range case instead.

Adjust the exhaustive nowrap tests to test both 5 bit and 1 bit
types.

Fixes https://github.com/llvm/llvm-project/issues/59301.

1 files changed, 3 insertions, 7 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 553e565..bae1e55 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -258,10 +258,9 @@ static ConstantRange makeExactMulNUWRegion(const APInt &V) {
 
 /// Exact mul nsw region for single element RHS.
 static ConstantRange makeExactMulNSWRegion(const APInt &V) {
-  // Handle special case for 0, -1 and 1. See the last for reason why we
-  // specialize -1 and 1.
+  // Handle 0 and -1 separately to avoid division by zero or overflow.
   unsigned BitWidth = V.getBitWidth();
-  if (V == 0 || V.isOne())
+  if (V == 0)
     return ConstantRange::getFull(BitWidth);
 
   APInt MinValue = APInt::getSignedMinValue(BitWidth);
@@ -278,10 +277,7 @@ static ConstantRange makeExactMulNSWRegion(const APInt &V) {
     Lower = APIntOps::RoundingSDiv(MinValue, V, APInt::Rounding::UP);
     Upper = APIntOps::RoundingSDiv(MaxValue, V, APInt::Rounding::DOWN);
   }
-  // ConstantRange ctor take a half inclusive interval [Lower, Upper + 1).
-  // Upper + 1 is guaranteed not to overflow, because |divisor| > 1. 0, -1,
-  // and 1 are already handled as special cases.
-  return ConstantRange(Lower, Upper + 1);
+  return ConstantRange::getNonEmpty(Lower, Upper + 1);
 }
 
 ConstantRange