[InstSimplify] use any-zero matcher for fcmp folds

The m_APFloat matcher does not work with anything but strict
splat vector constants, so we could miss these folds and then
trigger an assertion in instcombine:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13201

The previous attempt at this in rL354406 had a logic bug that
actually triggered a regression test failure, but I failed to
notice it the first time.

llvm-svn: 354467

1 files changed, 25 insertions, 22 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 843b3e97c07..ed857ddbc78 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3648,6 +3648,8 @@ static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
   }
 
   // Handle fcmp with constant RHS.
+  // TODO: Use match with a specific FP value, so these work with vectors with
+  // undef lanes.
   const APFloat *C;
   if (match(RHS, m_APFloat(C))) {
     // Check whether the constant is an infinity.
@@ -3676,28 +3678,7 @@ static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
         }
       }
     }
-    if (C->isZero()) {
-      switch (Pred) {
-      case FCmpInst::FCMP_OGE:
-        if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
-          return getTrue(RetTy);
-        break;
-      case FCmpInst::FCMP_UGE:
-        if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
-          return getTrue(RetTy);
-        break;
-      case FCmpInst::FCMP_ULT:
-        if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
-          return getFalse(RetTy);
-        break;
-      case FCmpInst::FCMP_OLT:
-        if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
-          return getFalse(RetTy);
-        break;
-      default:
-        break;
-      }
-    } else if (C->isNegative()) {
+    if (C->isNegative() && !C->isNegZero()) {
       assert(!C->isNaN() && "Unexpected NaN constant!");
       // TODO: We can catch more cases by using a range check rather than
       //       relying on CannotBeOrderedLessThanZero.
@@ -3721,6 +3702,28 @@ static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
       }
     }
   }
+  if (match(RHS, m_AnyZeroFP())) {
+    switch (Pred) {
+    case FCmpInst::FCMP_OGE:
+      if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
+        return getTrue(RetTy);
+      break;
+    case FCmpInst::FCMP_UGE:
+      if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
+        return getTrue(RetTy);
+      break;
+    case FCmpInst::FCMP_ULT:
+      if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
+        return getFalse(RetTy);
+      break;
+    case FCmpInst::FCMP_OLT:
+      if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
+        return getFalse(RetTy);
+      break;
+    default:
+      break;
+    }
+  }
 
   // If the comparison is with the result of a select instruction, check whether
   // comparing with either branch of the select always yields the same value.