+ Add unit test.

+ Remove duplicate False assignment in negated equality comparison.

Author: nhat-nguyen

lib/Backend/LowerMDShared.cpp

@@ -2683,9 +2683,10 @@ void LowererMD::GenerateFastCmXx(IR::Instr *instr)
     }
 
     bool isNegOpt = instr->m_opcode == Js::OpCode::CmNeq_A || instr->m_opcode == Js::OpCode::CmSrNeq_A;
+    bool initDstToFalse = true;
     if (isIntDst)
     {
-        // Fast path for float src when destination is type specialized to int
+        // Fast path for int src with destination type specialized to int
         // reg = MOV 0 will get peeped to XOR reg, reg which sets the flags.
         // Put the MOV before the CMP, but use a tmp if dst == src1/src2
         if (dst->IsEqual(src1) || dst->IsEqual(src2))
@@ -2705,7 +2706,7 @@ void LowererMD::GenerateFastCmXx(IR::Instr *instr)
     }
     else if (isFloatSrc)
     {
-        // Fast path for float src when destination is not type specialized to int
+        // Fast path for float src when destination is a var
         // Assign default value for destination in case either src is NaN
         Assert(dst->IsVar());
         if (isNegOpt)
@@ -2715,6 +2716,7 @@ void LowererMD::GenerateFastCmXx(IR::Instr *instr)
         else
         {
             opnd = this->m_lowerer->LoadLibraryValueOpnd(instr, LibraryValue::ValueFalse);
+            initDstToFalse = false;
         }
         Lowerer::InsertMove(tmp, opnd, done);
     }
@@ -2748,7 +2750,9 @@ void LowererMD::GenerateFastCmXx(IR::Instr *instr)
         done->InsertBefore(newInstr);
     }
 
-    if (!isIntDst)
+    // For all cases where the operator is a comparison, we do not want to emit False value
+    // since it has already been generated in the if block before.
+    if (!isIntDst && initDstToFalse)
     {
         opnd = this->m_lowerer->LoadLibraryValueOpnd(instr, LibraryValue::ValueFalse);
         Lowerer::InsertMove(tmp, opnd, done);

test/Basics/FloatComparison.js

@@ -0,0 +1,64 @@
+WScript.LoadScriptFile("..\\UnitTestFramework\\UnitTestFramework.js");
+
+// This tests the fast path for cmxx where either src is type specialized to float
+var tests = [
+    {
+        name: "NaN equality test",
+        body: function() {
+            assert.isTrue(NaN !== NaN);
+            assert.isTrue(NaN !== 0.5);
+            assert.isTrue(0.5 !== NaN);
+        
+            assert.isTrue(NaN != NaN);
+            assert.isTrue(NaN != 0.5);
+            assert.isTrue(0.5 != NaN);
+        
+            assert.isFalse(NaN === NaN);
+            assert.isFalse(NaN === 0.5);
+            assert.isFalse(0.5 === NaN);
+        
+            assert.isFalse(NaN == NaN);
+            assert.isFalse(NaN == 0.5);
+            assert.isFalse(0.5 == NaN);
+
+            assert.isFalse(NaN > 0.5);
+            assert.isFalse(NaN >= 0.5);
+            assert.isFalse(NaN < 0.5);
+            assert.isFalse(NaN <= 0.5);
+        }
+    },
+    {
+        name: "Type coercion test",
+        body: function() {
+            assert.isTrue('0.5' == 0.5);
+            assert.isFalse('0.5' === 0.5);
+            assert.isFalse('NaN' == NaN);
+            assert.isTrue('NaN' != NaN);
+        }
+    },
+    {
+        name: "int vs. float",
+        body: function() {
+            assert.isFalse(5 == 0.5);
+            assert.isTrue(5 != 0.5);
+            assert.isFalse(5 === 0.5);
+            assert.isTrue(5 !== 0.5);
+        }
+    },
+    {
+        name: "object vs. float",
+        body: function() {
+            assert.isFalse({} == 0.5);
+            assert.isFalse({} === 0.5);
+            assert.isTrue({} != 0.5);
+            assert.isTrue({} !== 0.5);
+        
+            assert.isFalse({} > 0.5);
+            assert.isFalse({} >= 0.5);
+            assert.isFalse({} < 0.5);
+            assert.isFalse({} <= 0.5);
+        }
+    }
+];
+
+testRunner.runTests(tests, { verbose: WScript.Arguments[0] != "summary" });

test/Basics/rlexe.xml

@@ -337,4 +337,10 @@
       <tags>exclude_test,exclude_jshost</tags>
     </default>
   </test>
+  <test>
+    <default>
+      <files>FloatComparison.js</files>
+      <compile-flags>-args summary -endargs</compile-flags>
+    </default>
+  </test>
 </regress-exe>