MIPS: Fix register usage in softfloat code path.

BUG=none
TEST=mjsunit/math-floor-part2.js

Review URL: https://codereview.chromium.org/12413032
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14099 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/code-stubs-mips.cc

@@ -684,6 +684,8 @@ void FloatingPointHelper::LoadNumber(MacroAssembler* masm,
                                      Register scratch1,
                                      Register scratch2,
                                      Label* not_number) {
+  ASSERT(!object.is(dst1) && !object.is(dst2));
+
   __ AssertRootValue(heap_number_map,
                      Heap::kHeapNumberMapRootIndex,
                      "HeapNumberMap register clobbered.");
@@ -878,6 +880,10 @@ void FloatingPointHelper::LoadNumberAsInt32Double(MacroAssembler* masm,
   ASSERT(!heap_number_map.is(object) &&
          !heap_number_map.is(scratch1) &&
          !heap_number_map.is(scratch2));
+  // ARM uses pop/push and Ldlr to save dst_* and probably object registers in
+  // softfloat path. On MIPS there is no ldlr, 1st lw instruction may overwrite
+  // object register making the 2nd lw invalid.
+  ASSERT(!object.is(dst_mantissa) && !object.is(dst_exponent));
 
   Label done, obj_is_not_smi;
 
@@ -914,49 +920,24 @@ void FloatingPointHelper::LoadNumberAsInt32Double(MacroAssembler* masm,
     if (destination == kCoreRegisters) {
       __ Move(dst_mantissa, dst_exponent, double_dst);
     }
-
   } else {
-    ASSERT(!scratch1.is(object) && !scratch2.is(object));
     // Load the double value in the destination registers.
-    bool save_registers = object.is(dst_mantissa) || object.is(dst_exponent);
-    if (save_registers) {
-      // Save both output registers, because the other one probably holds
-      // an important value too.
-      __ Push(dst_exponent, dst_mantissa);
-    }
     __ lw(dst_exponent, FieldMemOperand(object, HeapNumber::kExponentOffset));
     __ lw(dst_mantissa, FieldMemOperand(object, HeapNumber::kMantissaOffset));
 
     // Check for 0 and -0.
-    Label zero;
     __ And(scratch1, dst_exponent, Operand(~HeapNumber::kSignMask));
     __ Or(scratch1, scratch1, Operand(dst_mantissa));
-    __ Branch(&zero, eq, scratch1, Operand(zero_reg));
+    __ Branch(&done, eq, scratch1, Operand(zero_reg));
 
     // Check that the value can be exactly represented by a 32-bit integer.
     // Jump to not_int32 if that's not the case.
-    Label restore_input_and_miss;
     DoubleIs32BitInteger(masm, dst_exponent, dst_mantissa, scratch1, scratch2,
-                         &restore_input_and_miss);
+                         not_int32);
 
     // dst_* were trashed. Reload the double value.
-    if (save_registers) {
-      __ Pop(dst_exponent, dst_mantissa);
-    }
     __ lw(dst_exponent, FieldMemOperand(object, HeapNumber::kExponentOffset));
     __ lw(dst_mantissa, FieldMemOperand(object, HeapNumber::kMantissaOffset));
-    __ Branch(&done);
-
-    __ bind(&restore_input_and_miss);
-    if (save_registers) {
-      __ Pop(dst_exponent, dst_mantissa);
-    }
-    __ Branch(not_int32);
-
-    __ bind(&zero);
-    if (save_registers) {
-      __ Drop(2);
-    }
   }
 
   __ bind(&done);
@@ -2707,16 +2688,20 @@ void BinaryOpStub_GenerateFPOperation(MacroAssembler* masm,
               masm, destination, right, f14, a2, a3, heap_number_map,
               scratch1, scratch2, fail);
         }
+        // Use scratch3 as left in LoadNumber functions to avoid overwriting of
+        // left (a0) register.
+        __ mov(scratch3, left);
+
         // Load left operand to f12 or a0/a1. This keeps a0/a1 intact if it
         // jumps to |miss|.
         if (left_type == BinaryOpIC::INT32) {
           FloatingPointHelper::LoadNumberAsInt32Double(
-              masm, left, destination, f12, f16, a0, a1, heap_number_map,
+              masm, scratch3, destination, f12, f16, a0, a1, heap_number_map,
               scratch1, scratch2, f2, miss);
         } else {
           Label* fail = (left_type == BinaryOpIC::NUMBER) ? miss : not_numbers;
           FloatingPointHelper::LoadNumber(
-              masm, destination, left, f12, a0, a1, heap_number_map,
+              masm, destination, scratch3, f12, a0, a1, heap_number_map,
               scratch1, scratch2, fail);
         }
       }