Fix sysdeps/ieee754/dbl-64/mpa.c for -Wuninitialized [committed]

[Carlos O'Donell]

On 05/21/2015 07:07 PM, Joseph Myers wrote:
> If you remove the "override CFLAGS += -Wno-uninitialized" in
> math/Makefile, one of the errors you get is:
> 
> ../sysdeps/ieee754/dbl-64/mpa.c: In function '__mp_dbl.part.0':
> ../sysdeps/ieee754/dbl-64/mpa.c:183:5: error: 'c' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    c *= X[0];
> 
> The problem is that the p < 5 case initializes c if p is 1, 2, 3 or 4
> but not otherwise, and in fact p is positive for all calls to this
> function so the uninitialized case can't actually occur.  This patch
> replaces the "if (p == 4)" last case with a comment so the compiler
> can see that all paths do initialize c.

Just out of curiosity, did this result in better generated code?

c.