MIPS: Enable logical shift right and bitwise And matching to Ext, Dext.

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

Index: src/compiler/mips/instruction-selector-mips.cc
diff --git a/src/compiler/mips/instruction-selector-mips.cc b/src/compiler/mips/instruction-selector-mips.cc
index 961213afee9401e190ee85506e0e81f672ca43c5..9df0af6cb989f264532ea4e228bc77c9ffcdecf4 100644
--- a/src/compiler/mips/instruction-selector-mips.cc
+++ b/src/compiler/mips/instruction-selector-mips.cc
@@ -252,6 +252,38 @@ void InstructionSelector::VisitStore(Node* node) {
 
 
 void InstructionSelector::VisitWord32And(Node* node) {
+  MipsOperandGenerator g(this);
+  Int32BinopMatcher m(node);
+  if (m.left().IsWord32Shr() && CanCover(node, m.left().node()) &&
+      m.right().HasValue()) {
+    uint32_t mask = m.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)) {
+      // The mask must be contiguous, and occupy the least-significant bits.
+      DCHECK_EQ(0u, base::bits::CountTrailingZeros32(mask));
+
+      // Select Ext for And(Shr(x, imm), mask) where the mask is in the least
+      // significant bits.
+      Int32BinopMatcher mleft(m.left().node());
+      if (mleft.right().HasValue()) {
+        // Any shift value can match; int32 shifts use `value % 32`.
+        uint32_t lsb = mleft.right().Value() & 0x1f;
+
+        // Ext cannot extract bits past the register size, however since
+        // shifting the original value would have introduced some zeros we can
+        // still use Ext with a smaller mask and the remaining bits will be
+        // zeros.
+        if (lsb + mask_width > 32) mask_width = 32 - lsb;
+
+        Emit(kMipsExt, g.DefineAsRegister(node),
+             g.UseRegister(mleft.left().node()), g.TempImmediate(lsb),
+             g.TempImmediate(mask_width));
+        return;
+      }
+      // Other cases fall through to the normal And operation.
+    }
+  }
   VisitBinop(this, node, kMipsAnd);
 }
 
@@ -272,6 +304,26 @@ void InstructionSelector::VisitWord32Shl(Node* 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()) {
+      // Select Ext for Shr(And(x, mask), imm) where the result of the mask is
+      // shifted into the least-significant bits.
+      uint32_t mask = (mleft.right().Value() >> lsb) << lsb;
+      unsigned mask_width = base::bits::CountPopulation32(mask);
+      unsigned mask_msb = base::bits::CountLeadingZeros32(mask);
+      if ((mask_msb + mask_width + lsb) == 32) {
+        MipsOperandGenerator g(this);
+        DCHECK_EQ(lsb, base::bits::CountTrailingZeros32(mask));
+        Emit(kMipsExt, g.DefineAsRegister(node),
+             g.UseRegister(mleft.left().node()), g.TempImmediate(lsb),
+             g.TempImmediate(mask_width));
+        return;
+      }
+    }
+  }
   VisitRRO(this, kMipsShr, node);
 }