http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50938
Bug #: 50938
Summary: x86 alloca adds 15 twice
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: i...@airs.com
Using alloca on x86 requires that the return value be aligned to a 16-byte
(boundary). So code needs to add 15 to the size and then do & ~15. However,
compile this file:
extern void bar (char *);
void
foo (int n)
{
bar (__builtin_alloca (n));
}
The generated code adds 30, not 15. That is, the adjustment is made twice.
This works but wastes stack space.
The code in allocate_dynamic_stack_space in explow.c has become rather
convoluted and needs to be cleaned up to make this work. E.g., it does #if
defined (STACK_POINTER_OFFSET), but defaults.h ensures that
STACK_POINTER_OFFSET is always defined.
