Hello,
Compiling a big proprietary Ada source base with gcc 4.5 on x86-solaris
exposed misbehavior like
received signal SIGSEGV, Segmentation fault.
in allocno_priority_compare_func (v1p=0x21b0ce4, v2p=0x21b0cec)
at ../../src/gcc/ira-color.c:1745
1745 pri1 = allocno_priorities[ALLOCNO_NUM (a1)];
Very similar to what was reported as PR/44763 on existing testcases.
This turned out to be caused by a glitch with respect to possible overflows in
allocno_priority_compare_func:
<< pri1 = allocno_priorities[ALLOCNO_NUM (a1)];
pri2 = allocno_priorities[ALLOCNO_NUM (a2)];
if (pri2 - pri1)
return pri2 - pri1;
>>
The case we had ended up here with
p2 = 247786560, p1 = -1982292480
so p2> p1, but the function computed otherwise (p2-p1 = -2064888256).
This, in turn, lead to inconsistencies in the ordering relationship,
which the x86-solaris qsort implementation dislikes.
The attached patch is a proposal to address this by replacing the difference
computation by a comparison, factored out in a macro to allow reuse in other
places (not in this patch) and provide a clean spot for a general comment.
This fixed the observed SEGV with 4.5 and bootstrapped on i386-solaris. Was
also bootstrapped and regression tested for mainline on both sparc-solaris
and x86_64-linux.
OK ?