Fix constant folding of %_IsMinusZero.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/190793015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19762 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -3145,8 +3145,8 @@ bool HCompareMinusZeroAndBranch::KnownSuccessorBlock(HBasicBlock** block) {
     if (constant->HasDoubleValue()) {
       *block = IsMinusZero(constant->DoubleValue())
           ? FirstSuccessor() : SecondSuccessor();
+      return true;
     }
-    return true;
   }
   if (value()->representation().IsSmiOrInteger32()) {
     // A Smi or Integer32 cannot contain minus zero.

test/mjsunit/constant-fold-control-instructions.js

@@ -34,6 +34,10 @@ function test() {
 
   assertTrue(%_IsSpecObject(new Date()));
   assertFalse(%_IsSpecObject(1));
+
+  assertTrue(%_IsMinusZero(-0.0));
+  assertFalse(%_IsMinusZero(1));
+  assertFalse(%_IsMinusZero(""));
 }