[ConstantRange] Rename a method and add more doc

Rename makeNoWrapRegion to a more obvious makeGuaranteedNoWrapRegion,
and add a comment about the counter-intuitive aspects of the function.
This is to help prevent cases like PR26628.

llvm-svn: 261532

1 files changed, 4 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 07d72f5ee20..f1f57c6fbd6 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -1969,15 +1969,14 @@ StrengthenNoWrapFlags(ScalarEvolution *SE, SCEVTypes Type,
 
     const APInt &C = cast<SCEVConstant>(Ops[0])->getAPInt();
     if (!(SignOrUnsignWrap & SCEV::FlagNSW)) {
-      auto NSWRegion =
-        ConstantRange::makeNoWrapRegion(Instruction::Add, C, OBO::NoSignedWrap);
+      auto NSWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
+          Instruction::Add, C, OBO::NoSignedWrap);
       if (NSWRegion.contains(SE->getSignedRange(Ops[1])))
         Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
     }
     if (!(SignOrUnsignWrap & SCEV::FlagNUW)) {
-      auto NUWRegion =
-        ConstantRange::makeNoWrapRegion(Instruction::Add, C,
-                                        OBO::NoUnsignedWrap);
+      auto NUWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
+          Instruction::Add, C, OBO::NoUnsignedWrap);
       if (NUWRegion.contains(SE->getUnsignedRange(Ops[1])))
         Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
     }