PPC: [turbofan] Change TruncateFloat32ToUint64 to TryTruncateFloat32ToUint64.

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 550cb230a947f17681484e2c53bd7ec347afdbe8..60b73aee8127bbc498ba0d74ba1e1df0c749c741 100644
--- a/src/compiler/ppc/code-generator-ppc.cc
+++ b/src/compiler/ppc/code-generator-ppc.cc
@@ -1191,18 +1191,27 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
 #if V8_TARGET_ARCH_PPC64
     case kPPC_DoubleToUint64: {
       bool check_conversion = (i.OutputCount() > 1);
+      Label done;
       if (check_conversion) {
+        // Set 2nd output to zero if conversion fails.
+        // We must check explicitly for negative values here since the
+        // conversion instruction rounds the input toward zero before
+        // checking for validity (otherwise, values between -1 and 0
+        // would produce incorrect results).
+        __ li(i.OutputRegister(1), Operand::Zero());
+        __ fcmpu(i.InputDoubleRegister(0), kDoubleRegZero);
+        __ blt(&done);
         __ mtfsb0(VXCVI);  // clear FPSCR:VXCVI bit
       }
       __ ConvertDoubleToUnsignedInt64(i.InputDoubleRegister(0),
                                       i.OutputRegister(0), kScratchDoubleReg);
       if (check_conversion) {
-        // Set 2nd output to zero if conversion fails.
         CRBit crbit = static_cast<CRBit>(VXCVI % CRWIDTH);
         __ mcrfs(cr7, VXCVI);  // extract FPSCR field containing VXCVI into cr7
         __ li(i.OutputRegister(1), Operand(1));
         __ isel(i.OutputRegister(1), r0, i.OutputRegister(1),
                 v8::internal::Assembler::encode_crbit(cr7, crbit));
+        __ bind(&done);
       }
       DCHECK_EQ(LeaveRC, i.OutputRCBit());
       break;