PPC: clear high 32 bits from the result of mulhw.

The hight 32 bits of the result of mulhw are undefined and need
to be cleared manually.

Change-Id: I0e746898aa26a7970ab59b89c374afd1377028ea
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2347208Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#69318}

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

@@ -1515,12 +1515,18 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       }
       break;
     case kPPC_MulHigh32:
-      __ mulhw(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1),
-               i.OutputRCBit());
+      __ mulhw(ip, i.InputRegister(0), i.InputRegister(1), i.OutputRCBit());
+      // High 32 bits are undefined and need to be cleared.
+      __ li(r0, Operand(-1));
+      __ clrldi(r0, r0, Operand(32));
+      __ and_(i.OutputRegister(), ip, r0);
       break;
     case kPPC_MulHighU32:
-      __ mulhwu(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1),
-                i.OutputRCBit());
+      __ mulhwu(ip, i.InputRegister(0), i.InputRegister(1), i.OutputRCBit());
+      // High 32 bits are undefined and need to be cleared.
+      __ li(r0, Operand(-1));
+      __ clrldi(r0, r0, Operand(32));
+      __ and_(i.OutputRegister(), ip, r0);
       break;
     case kPPC_MulDouble:
       ASSEMBLE_FLOAT_BINOP_RC(fmul, MiscField::decode(instr->opcode()));