Fully implement integer modulo in intrinsifier, fall-through only for throwing exceptions. Also int…

runtime/vm/intrinsifier_ia32.cc

Index: runtime/vm/intrinsifier_ia32.cc
===================================================================
--- runtime/vm/intrinsifier_ia32.cc	(revision 21658)
+++ runtime/vm/intrinsifier_ia32.cc	(working copy)
@@ -667,35 +667,107 @@
 }
 
 
+// Optimizations:
+// - result is 0 if:
+//   - left is 0
+//   - left equals right
+// - result is left if
+//   - left > 0 && left < right
+// EAX: Tagged left (dividend).
+// EBX: Tagged right (divisor).
+// EDX: Untagged result (remainder).
+void EmitRemainderOperation(Assembler* assembler) {
+  Label return_zero, modulo;
+  // Check for quick zero results.
+  __ cmpl(EAX, Immediate(0));
+  __ j(EQUAL, &return_zero, Assembler::kNearJump);
+  __ cmpl(EAX, EBX);
+  __ j(EQUAL, &return_zero, Assembler::kNearJump);
+
+  // Check if result equals left.
+  __ cmpl(EAX, Immediate(0));
+  __ j(LESS, &modulo, Assembler::kNearJump);
+  // left is positive.
+  __ cmpl(EAX, EBX);
+  __ j(GREATER, &modulo,  Assembler::kNearJump);
+  // left is less than right, result is left (EAX).
+  __ ret();
+
+  __ Bind(&return_zero);
+  __ xorl(EAX, EAX);
+  __ ret();
+
+  __ Bind(&modulo);
+  __ SmiUntag(EBX);
+  __ SmiUntag(EAX);
+  __ cdq();
+  __ idivl(EBX);
+}
+
+
+// Implementation:
+//  res = left % right;
+//  if (res < 0) {
+//    if (right < 0) {
+//      res = res - right;
+//    } else {
+//      res = res + right;
+//    }
+//  }
 bool Intrinsifier::Integer_modulo(Assembler* assembler) {
-  Label fall_through, return_zero, try_modulo;
+  Label fall_through, subtract;
   TestBothArgumentsSmis(assembler, &fall_through);
   // EAX: right argument (divisor)
+  __ movl(EBX, EAX);
+  __ movl(EAX, Address(ESP, + 2 * kWordSize));  // Left argument (dividend).
+  // EAX: Tagged left (dividend).
+  // EBX: Tagged right (divisor).
   // Check if modulo by zero -> exception thrown in main function.
+  __ cmpl(EBX, Immediate(0));
+  __ j(EQUAL, &fall_through, Assembler::kNearJump);
+  EmitRemainderOperation(assembler);
+  // Untagged remainder result in EDX.
+  Label done;
+  __ movl(EAX, EDX);
   __ cmpl(EAX, Immediate(0));
-  __ j(EQUAL, &fall_through,  Assembler::kNearJump);
-  __ movl(EBX, Address(ESP, + 2 * kWordSize));  // Left argument (dividend).
+  __ j(GREATER_EQUAL, &done, Assembler::kNearJump);
+  // Result is negative, adjust it.
   __ cmpl(EBX, Immediate(0));
-  __ j(LESS, &fall_through, Assembler::kNearJump);
-  __ cmpl(EBX, EAX);
-  __ j(EQUAL, &return_zero, Assembler::kNearJump);
-  __ j(GREATER, &try_modulo, Assembler::kNearJump);
-  __ movl(EAX, EBX);  // Return dividend as it is smaller than divisor.
+  __ j(LESS, &subtract, Assembler::kNearJump);
+  __ addl(EAX, EBX);
+  __ SmiTag(EAX);
   __ ret();
-  __ Bind(&return_zero);
-  __ xorl(EAX, EAX);  // Return zero.
+
+  __ Bind(&subtract);
+  __ subl(EAX, EBX);
+
+  __ Bind(&done);
+  // The remainder of two Smi-s is always a Smi, no overflow check needed.
+  __ SmiTag(EAX);
   __ ret();
-  __ Bind(&try_modulo);
-  // EAX: right (non-null divisor).
+
+  __ Bind(&fall_through);
+  return false;
+}
+
+
+bool Intrinsifier::Integer_remainder(Assembler* assembler) {
+  Label fall_through;
+  TestBothArgumentsSmis(assembler, &fall_through);
+  // EAX: right argument (divisor)
   __ movl(EBX, EAX);
-  __ SmiUntag(EBX);
   __ movl(EAX, Address(ESP, + 2 * kWordSize));  // Left argument (dividend).
-  __ SmiUntag(EAX);
-  __ cdq();
-  __ idivl(EBX);
+  // EAX: Tagged left (dividend).
+  // EBX: Tagged right (divisor).
+  // Check if modulo by zero -> exception thrown in main function.
+  __ cmpl(EBX, Immediate(0));
+  __ j(EQUAL, &fall_through, Assembler::kNearJump);
+  EmitRemainderOperation(assembler);
+  // Untagged remainder result in EDX.
   __ movl(EAX, EDX);
   __ SmiTag(EAX);
   __ ret();
+
   __ Bind(&fall_through);
   return false;
 }