https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83292
Bug ID: 83292
Summary: __builtin_apply() triggers x87 stack exception on
32-bit x86
Product: gcc
Version: 7.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: achurch+gcc at achurch dot org
Target Milestone: ---
Calling a function with __builtin_apply() on 32-bit x86 causes the next x87
instruction to raise an x87 stack exception, as a side effect of mixing MMX
instructions (saving %mm[0-2]) and x87 instructions (fstp after the function
call, I presume to pop possible return values off the x87 stack).
Note that it's not possible to completely work around this with -mfpmath=sse
because fild is still used to load a 64-bit integer (s/int/long long/ in the
test case below).
The problem occurs at least as far back as GCC 5.4.0; I haven't tested earlier
versions.
Editing the generated assembly to bracket the __builtin_apply() code with
fstenv/fldenv seems to fix the problem.
Testcase:
==========================
void foo(void)
{
}
int main(void)
{
__builtin_apply(foo, __builtin_apply_args(), 0);
volatile int i = 1;
float f = i;
return f==1.0f ? 0 : 1;
}
==========================
