Index: build/toolchain.gypi |
diff --git a/build/toolchain.gypi b/build/toolchain.gypi |
index ee8efe13c4c0f8d960b8e39e354445bfd059c099..56b2e338eed352f3b2a95c408ad7fdfdb39653bf 100644 |
--- a/build/toolchain.gypi |
+++ b/build/toolchain.gypi |
@@ -811,6 +811,45 @@ |
}], |
['(OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris" \ |
or OS=="netbsd" or OS=="mac" or OS=="android" or OS=="qnx") and \ |
+ v8_target_arch=="ia32"', { |
+ # All floating-point computations on x87 happens in 80-bit |
+ # precision. Because the C and C++ language standards allow |
+ # the compiler to keep the floating-point values in higher |
+ # precision than what's specified in the source and doing so |
+ # is more efficient than constantly rounding up to 64-bit or |
+ # 32-bit precision as specified in the source, the compiler, |
+ # especially in the optimized mode, tries very hard to keep |
+ # values in x87 floating-point stack (in 80-bit precision) |
+ # as long as possible. This has important side effects, that |
+ # the real value used in computation may change depending on |
+ # how the compiler did the optimization - that is, the value |
+ # kept in 80-bit is different than the value rounded down to |
+ # 64-bit or 32-bit. There are possible compiler options to |
+ # make this behavior consistent (e.g. -ffloat-store would keep |
+ # all floating-values in the memory, thus force them to be |
+ # rounded to its original precision) but they have significant |
+ # runtime performance penalty. |
+ # |
+ # -mfpmath=sse -msse2 makes the compiler use SSE instructions |
+ # which keep floating-point values in SSE registers in its |
+ # native precision (32-bit for single precision, and 64-bit |
+ # for double precision values). This means the floating-point |
+ # value used during computation does not change depending on |
+ # how the compiler optimized the code, since the value is |
+ # always kept in its specified precision. |
+ # |
+ # Refer to http://crbug.com/348761 for rationale behind SSE2 |
+ # being a minimum requirement for 32-bit Linux builds and |
+ # http://crbug.com/313032 for an example where this has "bit" |
+ # us in the past. |
+ 'cflags': [ |
+ '-msse2', |
+ '-mfpmath=sse', |
+ '-mmmx', # Allows mmintrin.h for MMX intrinsics. |
+ ], |
+ }], |
+ ['(OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris" \ |
+ or OS=="netbsd" or OS=="mac" or OS=="android" or OS=="qnx") and \ |
(v8_target_arch=="arm" or v8_target_arch=="ia32" or \ |
v8_target_arch=="x87" or v8_target_arch=="mips" or \ |
v8_target_arch=="mipsel" or v8_target_arch=="ppc")', { |