MIPS[64]: Use immediates for kMips[64]Tst in code-generator-mips[64].cc

The patch optimizes the generation of code for kMips[64]Tst in code-generator-mips[64].cc.
We allow usage of immediate for kMips[64]Tst in VisitWordCompare in order to remove
an unnecessary immediate load to register. This fix is motivated by Richards benchark
in Octane benchmark suite, since it is used a lot there.

BUG=

Review-Url: https://codereview.chromium.org/2503833002
Cr-Commit-Position: refs/heads/master@{#40992}

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

@@ -1453,6 +1453,10 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
 
   // Match immediates on left or right side of comparison.
   if (g.CanBeImmediate(right, opcode)) {
+    if (opcode == kMipsTst) {
+      VisitCompare(selector, opcode, g.UseRegister(left), g.UseImmediate(right),
+                   cont);
+    } else {
       switch (cont->condition()) {
         case kEqual:
         case kNotEqual:
@@ -1475,8 +1479,13 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
           VisitCompare(selector, opcode, g.UseRegister(left),
                        g.UseRegister(right), cont);
       }
+    }
   } else if (g.CanBeImmediate(left, opcode)) {
     if (!commutative) cont->Commute();
+    if (opcode == kMipsTst) {
+      VisitCompare(selector, opcode, g.UseRegister(right), g.UseImmediate(left),
+                   cont);
+    } else {
       switch (cont->condition()) {
         case kEqual:
         case kNotEqual:
@@ -1499,6 +1508,7 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
           VisitCompare(selector, opcode, g.UseRegister(right),
                        g.UseRegister(left), cont);
       }
+    }
   } else {
     VisitCompare(selector, opcode, g.UseRegister(left), g.UseRegister(right),
                  cont);

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

@@ -1968,6 +1968,10 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
 
   // Match immediates on left or right side of comparison.
   if (g.CanBeImmediate(right, opcode)) {
+    if (opcode == kMips64Tst) {
+      VisitCompare(selector, opcode, g.UseRegister(left), g.UseImmediate(right),
+                   cont);
+    } else {
       switch (cont->condition()) {
         case kEqual:
         case kNotEqual:
@@ -1990,8 +1994,13 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
           VisitCompare(selector, opcode, g.UseRegister(left),
                        g.UseRegister(right), cont);
       }
+    }
   } else if (g.CanBeImmediate(left, opcode)) {
     if (!commutative) cont->Commute();
+    if (opcode == kMips64Tst) {
+      VisitCompare(selector, opcode, g.UseRegister(right), g.UseImmediate(left),
+                   cont);
+    } else {
       switch (cont->condition()) {
         case kEqual:
         case kNotEqual:
@@ -2014,6 +2023,7 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
           VisitCompare(selector, opcode, g.UseRegister(right),
                        g.UseRegister(left), cont);
       }
+    }
   } else {
     VisitCompare(selector, opcode, g.UseRegister(left), g.UseRegister(right),
                  cont);