[InstSimplify] More fcmp cases when comparing against negative constants.

Summary:
For known positive non-zero value X:
    fcmp uge X, -C => true
    fcmp ugt X, -C => true
    fcmp une X, -C => true
    fcmp oeq X, -C => false
    fcmp ole X, -C => false
    fcmp olt X, -C => false


Patch by Paul Walker.

Reviewers: majnemer, t.p.northover, spatel, RKSimon

Reviewed By: spatel

Subscribers: fhahn, llvm-commits

Differential Revision: https://reviews.llvm.org/D40012

llvm-svn: 319538

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 6bed2f3a901..145aa13dfc8 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3378,6 +3378,28 @@ static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
       default:
         break;
       }
+    } else if (C->isNegative()) {
+      assert(!C->isNaN() && "Unexpected NaN constant!");
+      // TODO: We can catch more cases by using a range check rather than
+      //       relying on CannotBeOrderedLessThanZero.
+      switch (Pred) {
+      case FCmpInst::FCMP_UGE:
+      case FCmpInst::FCMP_UGT:
+      case FCmpInst::FCMP_UNE:
+        // (X >= 0) implies (X > C) when (C < 0)
+        if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
+          return getTrue(RetTy);
+        break;
+      case FCmpInst::FCMP_OEQ:
+      case FCmpInst::FCMP_OLE:
+      case FCmpInst::FCMP_OLT:
+        // (X >= 0) implies !(X < C) when (C < 0)
+        if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
+          return getFalse(RetTy);
+        break;
+      default:
+        break;
+      }
     }
   }