[Pkg-chromium-maint] Bug#769836: [chromium-browser] Please use -fexcess-precision=standard or -ffloat-store instead of enabling sse2

[bastien ROUCARIÈS]

Package: chromium-browser
Severity: serious
version: 38.0.2125.101-4
justification: i386 package must be compiled for i586

According to gcc documentation and my experience [1]:

>The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and >correctness. All must be specifically enabled.
>
>-ffloat-store
>    Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory.
>
>    This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a double is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables.
>-fexcess-precision=style
>    This option allows further control over excess precision on machines where floating-point registers have more precision than the IEEE float and double types and the processor does not support operations rounding to those types. By default, -fexcess-precision=fast is in effect; this means that operations are carried out in the precision of the registers and that it is unpredictable when rounding to the types specified in the source code takes place. When compiling C, if -fexcess-precision=standard is specified then excess precision follows the rules specified in ISO C99; in particular, both casts and assignments cause values to be rounded to their semantic types (whereas -ffloat-store only affects assignments). This option is enabled by default for C if a strict conformance option such as -std=c99 is used.

>    -fexcess-precision=standard is not implemented for languages other than C, and has no effect if -funsafe-math-optimizations or -ffast-math is specified. On the x86, it also has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable. 

 [1] https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/Disappointments.html#Disappointments
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