MIPS[64]: Fix wrong optimization calculation on edge case in

InstructionSelector::VisitInt32Mul

TEST=cctest/test-run-machops/RunInt32MulAndInt32AddP,mjsunit/asm/int32mod-constant

Bug: 
Change-Id: Iaccfc0d0c981e7c7e2f8b06ff3812fe60d1f85d3
Reviewed-on: https://chromium-review.googlesource.com/574367Reviewed-by: Miran Karić <Miran.Karic@imgtec.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@imgtec.com>
Cr-Commit-Position: refs/heads/master@{#46707}

src/compiler/mips/instruction-selector-mips.cc

@@ -730,7 +730,7 @@ void InstructionSelector::VisitInt32Mul(Node* node) {
   MipsOperandGenerator g(this);
   Int32BinopMatcher m(node);
   if (m.right().HasValue() && m.right().Value() > 0) {
-    int32_t value = m.right().Value();
+    uint32_t value = static_cast<uint32_t>(m.right().Value());
     if (base::bits::IsPowerOfTwo(value)) {
       Emit(kMipsShl | AddressingModeField::encode(kMode_None),
            g.DefineAsRegister(node), g.UseRegister(m.left().node()),

src/compiler/mips64/instruction-selector-mips64.cc

@@ -979,7 +979,7 @@ void InstructionSelector::VisitInt32Mul(Node* node) {
   Mips64OperandGenerator g(this);
   Int32BinopMatcher m(node);
   if (m.right().HasValue() && m.right().Value() > 0) {
-    int32_t value = m.right().Value();
+    uint32_t value = static_cast<uint32_t>(m.right().Value());
     if (base::bits::IsPowerOfTwo(value)) {
       Emit(kMips64Shl | AddressingModeField::encode(kMode_None),
            g.DefineAsRegister(node), g.UseRegister(m.left().node()),
@@ -1036,7 +1036,7 @@ void InstructionSelector::VisitInt64Mul(Node* node) {
   Int64BinopMatcher m(node);
   // TODO(dusmil): Add optimization for shifts larger than 32.
   if (m.right().HasValue() && m.right().Value() > 0) {
-    int32_t value = static_cast<int32_t>(m.right().Value());
+    uint32_t value = static_cast<uint32_t>(m.right().Value());
     if (base::bits::IsPowerOfTwo(value)) {
       Emit(kMips64Dshl | AddressingModeField::encode(kMode_None),
            g.DefineAsRegister(node), g.UseRegister(m.left().node()),