MIPS:[turbofan] Match shift left and bitwise And with mask when possible.

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

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/adapters.h"
 #include "src/base/bits.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 312 matching lines @@
     MipsOperandGenerator g(this);
     Emit(kMipsNor, g.DefineAsRegister(node), g.UseRegister(m.left().node()),
          g.TempImmediate(0));
     return;
   }
   VisitBinop(this, node, kMipsXor);
 }
 
 
 void InstructionSelector::VisitWord32Shl(Node* node) {
+  Int32BinopMatcher m(node);

[titzer, 2015/12/04 09:26:58]

Can we get a comment that illustrates the pattern that this code matches?

[dusan.milosavljevic, 2015/12/04 12:50:58]

Done.

+  if (m.left().IsWord32And() && CanCover(node, m.left().node()) &&
+      m.right().IsInRange(1, 31)) {
+    MipsOperandGenerator g(this);
+    Int32BinopMatcher mleft(m.left().node());
+    if (mleft.right().HasValue()) {
+      uint32_t mask = mleft.right().Value();
+      uint32_t mask_width = base::bits::CountPopulation32(mask);
+      uint32_t mask_msb = base::bits::CountLeadingZeros32(mask);
+      if ((mask_width != 0) && (mask_msb + mask_width == 32)) {
+        uint32_t shift = m.right().Value();
+        DCHECK_EQ(0u, base::bits::CountTrailingZeros32(mask));
+        DCHECK_NE(0u, shift);
+        if ((shift + mask_width) >= 32) {
+          // If the mask is contiguous and reaches or extends beyond the top
+          // bit, only the shift is needed.
+          Emit(kMipsShl, g.DefineAsRegister(node),
+               g.UseRegister(mleft.left().node()),
+               g.UseImmediate(m.right().node()));
+          return;
+        }
+      }
+    }
+  }
   VisitRRO(this, kMipsShl, node);
 }
 
 
 void InstructionSelector::VisitWord32Shr(Node* node) {
   Int32BinopMatcher m(node);
   if (m.left().IsWord32And() && m.right().HasValue()) {
     uint32_t lsb = m.right().Value() & 0x1f;
     Int32BinopMatcher mleft(m.left().node());
     if (mleft.right().HasValue()) {
@@ skipping 883 matching lines @@
          MachineOperatorBuilder::kFloat32Max |
          MachineOperatorBuilder::kFloat32RoundDown |
          MachineOperatorBuilder::kFloat32RoundUp |
          MachineOperatorBuilder::kFloat32RoundTruncate |
          MachineOperatorBuilder::kFloat32RoundTiesEven;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8