MIPS:[turbofan] Use Ins, Dins to clear bits instead of And with inverted immediate.

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

Index: src/compiler/mips64/instruction-selector-mips64.cc
diff --git a/src/compiler/mips64/instruction-selector-mips64.cc b/src/compiler/mips64/instruction-selector-mips64.cc
index 90b3e37221d7388a97eb1060b7946901f2a6ebce..7fdd0745c67fe89b3a7ba18e6072a6fdb6beb394 100644
--- a/src/compiler/mips64/instruction-selector-mips64.cc
+++ b/src/compiler/mips64/instruction-selector-mips64.cc
@@ -295,6 +295,19 @@ void InstructionSelector::VisitWord32And(Node* node) {
       // Other cases fall through to the normal And operation.
     }
   }
+  if (m.right().HasValue()) {
+    uint32_t mask = m.right().Value();
+    uint32_t shift = base::bits::CountPopulation32(~mask);
+    uint32_t msb = base::bits::CountLeadingZeros32(~mask);
+    if (shift != 0 && shift != 32 && msb + shift == 32) {
+      // Insert zeros for (x >> K) << K => x & ~(2^K - 1) expression reduction
+      // and remove constant loading of invereted mask.

[paul.l..., 2015/12/01 17:49:34]

nit, inverted. Optional: maybe a comment mentioning DINS instruction is limited
to inserting within low 32-bits only? The code is right, but initial expectation
is that K could be up to 63. (And, if those cases were at all common in
practice, we could add DINSM, DINSU instructions. Might still be less than
loading 64-bit constant.)

[dusan.milosavljevic, 2015/12/01 21:55:54]

Done.

+      Emit(kMips64Ins, g.DefineSameAsFirst(node),
+           g.UseRegister(m.left().node()), g.TempImmediate(0),
+           g.TempImmediate(shift));
+      return;
+    }
+  }
   VisitBinop(this, node, kMips64And);
 }
 
@@ -332,6 +345,19 @@ void InstructionSelector::VisitWord64And(Node* node) {
       // Other cases fall through to the normal And operation.
     }
   }
+  if (m.right().HasValue()) {
+    uint64_t mask = m.right().Value();
+    uint32_t shift = base::bits::CountPopulation64(~mask);
+    uint32_t msb = base::bits::CountLeadingZeros64(~mask);
+    if (shift != 0 && shift < 32 && msb + shift == 64) {
+      // Insert zeros for (x >> K) << K => x & ~(2^K - 1) expression reduction
+      // and remove constant loading of invereted mask.
+      Emit(kMips64Dins, g.DefineSameAsFirst(node),
+           g.UseRegister(m.left().node()), g.TempImmediate(0),
+           g.TempImmediate(shift));
+      return;
+    }
+  }
   VisitBinop(this, node, kMips64And);
 }