On Fri, 22 Mar 2013, Jakub Jelinek wrote: > On Fri, Mar 22, 2013 at 11:06:53AM +0100, Richard Biener wrote: > > This fixes PR56434 - the use of BIGGEST_ALIGNMENT to annotate > > the pointer returned by malloc is wrong - BIGGEST_ALIGNMENT > > has nothing to do with the alignment guaranteed by the ABI > > for allocated memory. For example on x86_64 it depends on > > -mavx and thus can result in wrong code being generated. > > > > The following patch fixes it to use what we use on the > > GIMPLE level - MALLOC_ABI_ALIGNMENT. > > > > Ok for trunk? > > IMHO the change should be accompanied by defining MALLOC_ABI_ALIGNMENT > on at least a couple of popular targets. E.g. glibc > will guarantee at least 2 * sizeof (void *) alignment on all architectures, > and even if one uses some other malloc implementation, it should be better > ISO C99 conforming on Linux (perhaps ignoring long double type (known > to be non-conforming e.g. on ppc32) and _Decimal* types). > So, at least for Linux I'd say MALLOC_ABI_ALIGNMENT should be defined > as maximum alignment of long, long long, double and void *. > > Because, right now, MALLOC_ABI_ALIGNMENT is only defined to > non-__alignof__(char) on VMS.
I think the wrong-code fix is orthogonal to code improvements which will also trigger on the GIMPLE level (and where they will have a bigger impact). We can for example, in config/linux.h do #if OPTION_GLIBC #undef MALLOC_ABI_ALIGNMENT #define MALLOC_ABI_ALIGNMENT (2 * sizeof (void *)) #endif if that's what glibc really guarantees (does it maybe have a feature macro for this?) Richard. > > 2013-03-22 Richard Biener <rguent...@suse.de> > > > > PR middle-end/56434 > > * calls.c (expand_call): Use MALLOC_ABI_ALIGNMENT to annotate > > the pointer returned by calls with ECF_MALLOC set. > > > > Index: gcc/calls.c > > =================================================================== > > --- gcc/calls.c (revision 196899) > > +++ gcc/calls.c (working copy) > > @@ -3186,7 +3186,7 @@ expand_call (tree exp, rtx target, int i > > > > /* The return value from a malloc-like function is a pointer. */ > > if (TREE_CODE (rettype) == POINTER_TYPE) > > - mark_reg_pointer (temp, BIGGEST_ALIGNMENT); > > + mark_reg_pointer (temp, MALLOC_ABI_ALIGNMENT); > > > > emit_move_insn (temp, valreg); > > > > Jakub > > -- Richard Biener <rguent...@suse.de> SUSE / SUSE Labs SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746 GF: Jeff Hawn, Jennifer Guild, Felix Imend
