On x64 use 32bit idiv when possible instead of 64bit one.

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 afac01fb721262d969ad6a0cda78dfc1d0e6aac5..2dfed3a9f7a38f8d232f285840684f8209e2eb74 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -2328,13 +2328,40 @@ void BinarySmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       break;
     }
     case Token::kTRUNCDIV: {
-      // Handle divide by zero in runtime.
-      __ testq(right, right);
-      __ j(ZERO, deopt);
+      Label not_32bit, done;
+
+      Register temp = locs()->temp(0).reg();
       ASSERT(left == RAX);
       ASSERT((right != RDX) && (right != RAX));
-      ASSERT(locs()->temp(0).reg() == RDX);
+      ASSERT(temp == RDX);
       ASSERT(result == RAX);
+
+      // Handle divide by zero in runtime.
+      __ testq(right, right);
+      __ j(ZERO, deopt);
+
+      // Check if both operands fit into 32bits as idiv with 64bit operands
+      // requires twice as many cycles and has much higher latency.
+      // We are checking this before untagging them to avoid corner case
+      // dividing INT_MAX by -1 that raises exception because quotient is
+      // too large for 32bit register.
+      __ movsxl(temp, left);
+      __ cmpq(temp, left);
+      __ j(NOT_EQUAL, &not_32bit);
+      __ movsxl(temp, right);
+      __ cmpq(temp, right);
+      __ j(NOT_EQUAL, &not_32bit);
+
+      // Both operands are 31bit smis. Divide using 32bit idiv.
+      __ SmiUntag(left);
+      __ SmiUntag(right);
+      __ cdq();
+      __ idivl(right);
+      __ movsxl(result, result);
+      __ jmp(&done);
+
+      // Divide using 64bit idiv.
+      __ Bind(&not_32bit);
       __ SmiUntag(left);
       __ SmiUntag(right);
       __ cqo();  // Sign extend RAX -> RDX:RAX.
@@ -2343,6 +2370,7 @@ void BinarySmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       // case we cannot tag the result.
       __ cmpq(result, Immediate(0x4000000000000000));
       __ j(EQUAL, deopt);
+      __ Bind(&done);
       __ SmiTag(result);
       break;
     }