PPC: [turbofan] Introduce integer multiplication with overflow.

src/compiler/ppc/code-generator-ppc.cc

Index: src/compiler/ppc/code-generator-ppc.cc
diff --git a/src/compiler/ppc/code-generator-ppc.cc b/src/compiler/ppc/code-generator-ppc.cc
index 6da65c348559667fd14461b08a4667e5b1178570..e1503aeb1891b7f4acdfaabc6ea605ecd1977cc8 100644
--- a/src/compiler/ppc/code-generator-ppc.cc
+++ b/src/compiler/ppc/code-generator-ppc.cc
@@ -975,6 +975,11 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
     case kArchPrepareTailCall:
       AssemblePrepareTailCall();
       break;
+    case kArchComment: {
+      Address comment_string = i.InputExternalReference(0).address();
+      __ RecordComment(reinterpret_cast<const char*>(comment_string));
+      break;
+    }
     case kArchCallCFunction: {
       int const num_parameters = MiscField::decode(instr->opcode());
       if (instr->InputAt(0)->IsImmediate()) {
@@ -1300,6 +1305,12 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
                LeaveOE, i.OutputRCBit());
       break;
 #endif
+    case kPPC_Mul32WithHigh32:

[john.yan, 2016/07/16 03:57:48]

The reason why this fails is that output reg can be one of the input reg.
Therefore, mullw could be modifying one of the input reg, which causes mulhw to
produce incorrect output.

+      __ mullw(i.OutputRegister(0),
+               i.InputRegister(0), i.InputRegister(1));  // low
+      __ mulhw(i.OutputRegister(1),
+               i.InputRegister(0), i.InputRegister(1));  // high
+      break;

[john.yan, 2016/07/16 03:54:45]

Try this sequence here:
 +    case kPPC_Mul32WithHigh32:
 +      if (i.OutputRegister(0).is(i.InputRegister(0)) ||
 +          i.OutputRegister(0).is(i.InputRegister(1)) ||
 +          i.OutputRegister(1).is(i.InputRegister(0)) ||
 +          i.OutputRegister(1).is(i.InputRegister(1))) {
 +        __ mullw(kScratchReg,
 +                 i.InputRegister(0), i.InputRegister(1));  // low
 +        __ mulhw(i.OutputRegister(1),
 +                 i.InputRegister(0), i.InputRegister(1));  // high
 +        __ mr(i.OutputRegister(0), kScratchReg);
 +      } else {
 +        __ mullw(i.OutputRegister(0),
 +                 i.InputRegister(0), i.InputRegister(1));  // low
 +        __ mulhw(i.OutputRegister(1),
 +                 i.InputRegister(0), i.InputRegister(1));  // high
 +      }
 +      break;

     case kPPC_MulHigh32:
       __ mulhw(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1),
                i.OutputRCBit());