Speculate on bitwise operators.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
diff --git a/runtime/vm/intermediate_language_x64.cc b/runtime/vm/intermediate_language_x64.cc
index 4fc3b68d2845309a709d2ee451fe5ab1c93e408e..f872c21ad312a94cfa2cc6af393b535ddf37bba4 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -2879,8 +2879,9 @@ class CheckedSmiSlowPath : public SlowPathCode {
 
 LocationSummary* CheckedSmiOpInstr::MakeLocationSummary(Zone* zone,
                                                         bool opt) const {
+  bool is_shift = (op_kind() == Token::kSHL) || (op_kind() == Token::kSHR);
   const intptr_t kNumInputs = 2;
-  const intptr_t kNumTemps = 0;
+  const intptr_t kNumTemps = is_shift ? 1 : 0;
   LocationSummary* summary = new(zone) LocationSummary(
       zone, kNumInputs, kNumTemps, LocationSummary::kCallOnSlowPath);
   summary->set_in(0, Location::RequiresRegister());
@@ -2889,6 +2890,8 @@ LocationSummary* CheckedSmiOpInstr::MakeLocationSummary(Zone* zone,
     case Token::kADD:
     case Token::kSUB:
     case Token::kMUL:
+    case Token::kSHL:
+    case Token::kSHR:
       summary->set_out(0, Location::RequiresRegister());
       break;
     case Token::kBIT_OR:
@@ -2899,6 +2902,9 @@ LocationSummary* CheckedSmiOpInstr::MakeLocationSummary(Zone* zone,
     default:
       UNIMPLEMENTED();
   }
+  if (is_shift) {
+    summary->set_temp(0, Location::RegisterLocation(RCX));
+  }
   return summary;
 }
 
@@ -2955,6 +2961,40 @@ void CheckedSmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       ASSERT(left == result);
       __ xorq(result, right);
       break;
+    case Token::kSHL:
+      ASSERT(result != right);
+      ASSERT(locs()->temp(0).reg() == RCX);
+      __ cmpq(right, Immediate(Smi::RawValue(Smi::kBits)));
+      __ j(ABOVE_EQUAL, slow_path->entry_label());
+
+      __ movq(RCX, right);
+      __ SmiUntag(RCX);
+      __ movq(result, left);
+      __ shlq(result, RCX);
+      __ movq(TMP, result);
+      __ sarq(TMP, RCX);
+      __ cmpq(TMP, result);
+      __ j(NOT_EQUAL, slow_path->entry_label());
+      break;
+    case Token::kSHR: {
+      Label shift_count_ok;
+      ASSERT(result != right);
+      ASSERT(locs()->temp(0).reg() == RCX);
+      __ cmpq(right, Immediate(0));
+      __ j(LESS, slow_path->entry_label());

[Florian Schneider, 2016/11/11 18:12:20]

Can you use unsigned compare "right <
(unsigned)Smi::RawValue(kMaxSmiShiftCount)" to save one comparison? (applies to
other platforms as well)

[rmacnak, 2016/11/11 21:29:02]

Yes. As discussed offline this means something like 1 >> 100 would go to the
slow path, but we expect this is rare.

+
+      __ movq(RCX, right);
+      __ SmiUntag(RCX);
+      __ cmpq(RCX, Immediate(0x3F));
+      __ j(LESS_EQUAL, &shift_count_ok, Assembler::kNearJump);
+      __ movq(RCX, Immediate(0x3F));
+      __ Bind(&shift_count_ok);
+      __ movq(result, left);
+      __ SmiUntag(result);
+      __ sarq(result, RCX);
+      __ SmiTag(result);
+      break;
+    }
     default:
       UNIMPLEMENTED();
   }