[ConstantRange] Split makeICmpRegion in two.

Summary:
This change splits `makeICmpRegion` into `makeAllowedICmpRegion` and
`makeSatisfyingICmpRegion` with slightly different contracts.  The first
one is useful for determining what values some expression //may// take,
given that a certain `icmp` evaluates to true.  The second one is useful
for determining what values are guaranteed to //satisfy// a given
`icmp`.

Reviewers: nlewycky

Reviewed By: nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8345

llvm-svn: 232575

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index eec18b95fb8..91095cfe9ee 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -49,14 +49,15 @@ ConstantRange::ConstantRange(APIntMoveTy L, APIntMoveTy U)
          "Lower == Upper, but they aren't min or max value!");
 }
 
-ConstantRange ConstantRange::makeICmpRegion(unsigned Pred,
-                                            const ConstantRange &CR) {
+ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
+                                                   const ConstantRange &CR) {
   if (CR.isEmptySet())
     return CR;
 
   uint32_t W = CR.getBitWidth();
   switch (Pred) {
-    default: llvm_unreachable("Invalid ICmp predicate to makeICmpRegion()");
+  default:
+    llvm_unreachable("Invalid ICmp predicate to makeAllowedICmpRegion()");
     case CmpInst::ICMP_EQ:
       return CR;
     case CmpInst::ICMP_NE:
@@ -114,6 +115,16 @@ ConstantRange ConstantRange::makeICmpRegion(unsigned Pred,
   }
 }
 
+ConstantRange ConstantRange::makeSatisfyingICmpRegion(CmpInst::Predicate Pred,
+                                                      const ConstantRange &CR) {
+  // Follows from De-Morgan's laws:
+  //
+  // ~(~A union ~B) == A intersect B.
+  //
+  return makeAllowedICmpRegion(CmpInst::getInversePredicate(Pred), CR)
+      .inverse();
+}
+
 /// isFullSet - Return true if this set contains all of the elements possible
 /// for this data-type
 bool ConstantRange::isFullSet() const {