ARM: Tweak ECMAToInt32VFP to address regression on Nexus 4

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 0c21731770829628404c961b41f058fe45d45b75..634a2b4e668a78980452bd5c54dfe68056346dbc 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -2531,29 +2531,17 @@ void MacroAssembler::ECMAToInt32VFP(Register result,
          !scratch.is(input_low));
   ASSERT(!double_input.is(double_scratch));
 
-  Label overflow, out_of_range, negate, done;
+  Label out_of_range, negate, done;
 
+  vcvt_s32_f64(double_scratch.low(), double_input);
+  vmov(result, double_scratch.low());
+  sub(scratch, result, Operand(1));

[Rodolph Perfetta, 2013/03/14 11:57:58]

Maybe a comment saying we are testing for saturation (0x7fffffff and 0x80000000)
would be useful.

[hans, 2013/03/14 12:12:05]

Done.

+  cmp(scratch, Operand(0x7ffffffe));
+  b(lt, &done);
   vmov(input_low, input_high, double_input);
   Ubfx(scratch, input_high,
        HeapNumber::kExponentShift, HeapNumber::kExponentBits);
-  // Load scratch with exponent - 1. This is faster than loading
-  // with exponent because Bias + 1 = 1024 which is an *ARM* immediate value.
   sub(scratch, scratch, Operand(HeapNumber::kExponentBias + 1));

[Rodolph Perfetta, 2013/03/14 11:57:58]

I would leave the comment above.

[hans, 2013/03/14 12:12:05]

Done.

-  // Compare exponent with 31 (compare exponent - 1 with 30).
-  cmp(scratch, Operand(30));
-  b(ge, &overflow);
-  // Exponent is less than 31 so vcvt will never saturate.
-  // So, just return the result.
-  vcvt_s32_f64(double_scratch.low(), double_input);
-  vmov(result, double_scratch.low());
-  b(&done);
-
-  bind(&overflow);
-  // If exponent is greater than or equal to 84, the 32 less significant
-  // bits are 0s (2^84 = 1, 52 significant bits, 32 uncoded bits),
-  // the result is 0.
-  // This test also catch Nan and infinities which also return 0.
-  // Compare exponent with 84 (compare exponent - 1 with 83).
   cmp(scratch, Operand(83));

[Rodolph Perfetta, 2013/03/14 11:57:58]

ditto.

[hans, 2013/03/14 12:12:05]

Done.

   b(ge, &out_of_range);