[ValueTracking][ConstantRange] Distinguish low/high always overflow

In order to fold an always overflowing signed saturating add/sub,
we need to know in which direction the always overflow occurs.
This patch splits up AlwaysOverflows into AlwaysOverflowsLow and
AlwaysOverflowsHigh to pass through this information (but it is
not used yet).

Differential Revision: https://reviews.llvm.org/D62463

llvm-svn: 361858

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index d46ddc428b2..640063700e8 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3992,8 +3992,10 @@ static OverflowResult mapOverflowResult(ConstantRange::OverflowResult OR) {
   switch (OR) {
     case ConstantRange::OverflowResult::MayOverflow:
       return OverflowResult::MayOverflow;
-    case ConstantRange::OverflowResult::AlwaysOverflows:
-      return OverflowResult::AlwaysOverflows;
+    case ConstantRange::OverflowResult::AlwaysOverflowsLow:
+      return OverflowResult::AlwaysOverflowsLow;
+    case ConstantRange::OverflowResult::AlwaysOverflowsHigh:
+      return OverflowResult::AlwaysOverflowsHigh;
     case ConstantRange::OverflowResult::NeverOverflows:
       return OverflowResult::NeverOverflows;
   }