[ConstantRange] Calculate precise range for multiply by -1

These are pretty common in SCEV, so make sure we get a precise
result by mapping to the sub() operation.

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 74cc097..e9344a8 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -1095,6 +1095,20 @@ ConstantRange::multiply(const ConstantRange &Other) const {
   if (isEmptySet() || Other.isEmptySet())
     return getEmpty();
 
+  if (const APInt *C = getSingleElement()) {
+    if (C->isOne())
+      return Other;
+    if (C->isAllOnes())
+      return ConstantRange(APInt::getZero(getBitWidth())).sub(Other);
+  }
+
+  if (const APInt *C = Other.getSingleElement()) {
+    if (C->isOne())
+      return *this;
+    if (C->isAllOnes())
+      return ConstantRange(APInt::getZero(getBitWidth())).sub(*this);
+  }
+
   // Multiplication is signedness-independent. However different ranges can be
   // obtained depending on how the input ranges are treated. These different
   // ranges are all conservatively correct, but one might be better than the