[ConstantRange] Fix off by 1 bugs in UIToFP and SIToFP handling. (#86041)

We were passing the min and max values of the range to the ConstantRange
constructor, but the constructor expects the upper bound to 1 more than
the max value so we need to add 1.

We also need to use getNonEmpty so that passing 0, 0 to the constructor
creates a full range rather than an empty range. And passing smin,
smax+1 doesn't cause an assertion.

I believe this fixes at least some of the reason #79158 was reverted.

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 3394a1e..59e7a9f 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -746,7 +746,7 @@ ConstantRange ConstantRange::castOp(Instruction::CastOps CastOp,
       Min = Min.zext(ResultBitWidth);
       Max = Max.zext(ResultBitWidth);
     }
-    return ConstantRange(std::move(Min), std::move(Max));
+    return getNonEmpty(std::move(Min), std::move(Max) + 1);
   }
   case Instruction::SIToFP: {
     // TODO: use input range if available
@@ -757,7 +757,7 @@ ConstantRange ConstantRange::castOp(Instruction::CastOps CastOp,
       SMin = SMin.sext(ResultBitWidth);
       SMax = SMax.sext(ResultBitWidth);
     }
-    return ConstantRange(std::move(SMin), std::move(SMax));
+    return getNonEmpty(std::move(SMin), std::move(SMax) + 1);
   }
   case Instruction::FPTrunc:
   case Instruction::FPExt: