[turbofan] Introduce integer multiplication with overflow.

src/code-stubs.cc

Index: src/code-stubs.cc
diff --git a/src/code-stubs.cc b/src/code-stubs.cc
index f4ec29b65c98dd1c71807a0b2547b9eb3695ee1c..ca8bebe58efaab5669073ce76f9395cebd043314 100644
--- a/src/code-stubs.cc
+++ b/src/code-stubs.cc
@@ -1067,6 +1067,7 @@ compiler::Node* MultiplyStub::Generate(CodeStubAssembler* assembler,
 
   // Shared entry point for floating point multiplication.
   Label do_fmul(assembler);
+  Label end(assembler);

[Benedikt Meurer, 2016/07/12 04:09:28]

Nit: Can you rename this to return_result and add it to the preceeding line,
i.e.:

Label do_fmul(assembler), return_result(assembler);

[mvstanton, 2016/07/12 08:52:49]

Done.

   Variable var_lhs_float64(assembler, MachineRepresentation::kFloat64),
       var_rhs_float64(assembler, MachineRepresentation::kFloat64);
 
@@ -1074,7 +1075,8 @@ compiler::Node* MultiplyStub::Generate(CodeStubAssembler* assembler,
 
   // We might need to loop one or two times due to ToNumber conversions.
   Variable var_lhs(assembler, MachineRepresentation::kTagged),
-      var_rhs(assembler, MachineRepresentation::kTagged);
+      var_rhs(assembler, MachineRepresentation::kTagged),
+      var_result(assembler, MachineRepresentation::kTagged);
   Variable* loop_variables[] = {&var_lhs, &var_rhs};
   Label loop(assembler, 2, loop_variables);
   var_lhs.Bind(left);
@@ -1098,6 +1100,44 @@ compiler::Node* MultiplyStub::Generate(CodeStubAssembler* assembler,
       {
         // Both {lhs} and {rhs} are Smis. Convert them to double and multiply.
         // TODO(epertoso): use SmiMulWithOverflow once available.

[Benedikt Meurer, 2016/07/12 04:09:28]

Remove this TODO.

[mvstanton, 2016/07/12 08:52:49]

Done.

+        Node* lhs32 = assembler->SmiToWord32(lhs);
+        Node* rhs32 = assembler->SmiToWord32(rhs);
+        Node* pair = assembler->Int32MulWithOverflow(lhs32, rhs32);
+
+        Node* overflow = assembler->Projection(1, pair);
+
+        // Check if the multiplication overflowed.
+        Label if_overflow(assembler), if_notoverflow(assembler);

[Benedikt Meurer, 2016/07/12 04:09:28]

Make the if_overflow label deferred.

[mvstanton, 2016/07/12 08:52:49]

Done.

+        assembler->Branch(overflow, &if_overflow, &if_notoverflow);
+
+        assembler->Bind(&if_notoverflow);

[Benedikt Meurer, 2016/07/12 04:09:28]

Add braces around the actual blocks for improved readability.

[mvstanton, 2016/07/12 08:52:49]

Done.

+        // If the answer is zero, we may need to return -0.0, depending on the
+        // input.
+        Label answer_zero(assembler), answer_not_zero(assembler);
+        Node* answer = assembler->Projection(0, pair);
+        Node* zero = assembler->Int32Constant(0);
+        assembler->Branch(assembler->WordEqual(answer, zero), &answer_zero,
+                          &answer_not_zero);
+
+        assembler->Bind(&answer_not_zero);
+        var_result.Bind(assembler->ChangeInt32ToTagged(answer));
+        assembler->Goto(&end);
+
+        assembler->Bind(&answer_zero);
+        Node* or_result = assembler->Word32Or(lhs32, rhs32);
+        Label if_should_be_negative_zero(assembler),
+            if_should_be_zero(assembler);
+        assembler->Branch(assembler->Int32LessThan(or_result, zero),
+                          &if_should_be_negative_zero, &if_should_be_zero);
+        assembler->Bind(&if_should_be_negative_zero);
+        var_result.Bind(assembler->MinusZeroConstant());
+        assembler->Goto(&end);
+
+        assembler->Bind(&if_should_be_zero);
+        var_result.Bind(zero);
+        assembler->Goto(&end);
+
+        assembler->Bind(&if_overflow);
         var_lhs_float64.Bind(assembler->SmiToFloat64(lhs));
         var_rhs_float64.Bind(assembler->SmiToFloat64(rhs));
         assembler->Goto(&do_fmul);
@@ -1201,8 +1241,12 @@ compiler::Node* MultiplyStub::Generate(CodeStubAssembler* assembler,
     Node* value =
         assembler->Float64Mul(var_lhs_float64.value(), var_rhs_float64.value());
     Node* result = assembler->ChangeFloat64ToTagged(value);
-    return result;
+    var_result.Bind(result);
+    assembler->Goto(&end);
   }
+
+  assembler->Bind(&end);
+  return var_result.value();
 }
 
 // static