Re-apply r251050 with a for PR25421

The bug: I missed adding break statements in the switch / case.

Original commit message:

[SCEV] Teach SCEV some axioms about non-wrapping arithmetic

Summary:
 - A s<  (A + C)<nsw> if C >  0
 - A s<= (A + C)<nsw> if C >= 0
 - (A + C)<nsw> s<  A if C <  0
 - (A + C)<nsw> s<= A if C <= 0

Right now `C` needs to be a constant, but we can later generalize it to
be a non-constant if needed.

Reviewers: atrick, hfinkel, reames, nlewycky

Subscribers: sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D13686

llvm-svn: 252236

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 65125a7da5e..c180ce37e39 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -732,6 +732,14 @@ namespace llvm {
     bool isKnownPredicateWithRanges(ICmpInst::Predicate Pred,
                                     const SCEV *LHS, const SCEV *RHS);
 
+    /// Try to prove the condition described by "LHS Pred RHS" by ruling out
+    /// integer overflow.
+    ///
+    /// For instance, this will return true for "A s< (A + C)<nsw>" if C is
+    /// positive.
+    bool isKnownPredicateViaNoOverflow(ICmpInst::Predicate Pred,
+                                       const SCEV *LHS, const SCEV *RHS);
+
     /// Try to split Pred LHS RHS into logical conjunctions (and's) and try to
     /// prove them individually.
     bool isKnownPredicateViaSplitting(ICmpInst::Predicate Pred, const SCEV *LHS,