deps: V8: backport 3f071e3e7e15

Original commit message:

    PPC: Optimize clearing higher bits of mulhw/mulhwu

    Change-Id: Ie3e14a6ef4531349e81a8ae741bc7470c7e547ca
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2349468
    Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
    Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
    Cr-Commit-Position: refs/heads/master@{#69343}

Refs: v8/v8@3f071e3

PR-URL: nodejs#35036
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ash Cripps <ashley.cripps@ibm.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

common.gypi

@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.14',
+    'v8_embedder_string': '-node.15',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/src/compiler/backend/ppc/code-generator-ppc.cc

@@ -1515,12 +1515,14 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       }
       break;
     case kPPC_MulHigh32:
-      __ mulhw(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1),
-               i.OutputRCBit());
+      __ mulhw(r0, i.InputRegister(0), i.InputRegister(1), i.OutputRCBit());
+      // High 32 bits are undefined and need to be cleared.
+      __ clrldi(i.OutputRegister(), r0, Operand(32));
       break;
     case kPPC_MulHighU32:
-      __ mulhwu(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1),
-                i.OutputRCBit());
+      __ mulhwu(r0, i.InputRegister(0), i.InputRegister(1), i.OutputRCBit());
+      // High 32 bits are undefined and need to be cleared.
+      __ clrldi(i.OutputRegister(), r0, Operand(32));
       break;
     case kPPC_MulDouble:
       ASSEMBLE_FLOAT_BINOP_RC(fmul, MiscField::decode(instr->opcode()));