| Message ID | 34515865.Hv3Ka6M9TT@polaris |
|---|---|
| State | New |
| Headers | show |
On Tue, Jan 10, 2017 at 9:31 PM, Eric Botcazou <ebotcazou@adacore.com> wrote: > Hi, > > LRA generates an unaligned memory access for 32-bit SPARC on the attached > testcase when it is compiled with optimization. It's again the business of > paradoxical subregs of memory dealt with by simplify_operand_subreg: > > /* If we change the address for a paradoxical subreg of memory, the > address might violate the necessary alignment or the access might > be slow. So take this into consideration. We need not worry > about accesses beyond allocated memory for paradoxical memory > subregs as we don't substitute such equiv memory (see processing > equivalences in function lra_constraints) and because for spilled > pseudos we allocate stack memory enough for the biggest > corresponding paradoxical subreg. */ > if (!(MEM_ALIGN (reg) < GET_MODE_ALIGNMENT (mode) > && SLOW_UNALIGNED_ACCESS (mode, MEM_ALIGN (reg))) > || (MEM_ALIGN (reg) < GET_MODE_ALIGNMENT (innermode) > && SLOW_UNALIGNED_ACCESS (innermode, MEM_ALIGN (reg)))) > return true; > > However the code contains a small inaccuracy: it tests the old MEM (reg) which > has mode INNERMODE in the first branch of the condition instead of testing the > new MEM (subst) which has mode MODE. That's benign for little-endian targets > since the offset doesn't change, but not for big-endian ones where it changes > and thus also can change the alignment. > > The attached fix was bootstrapped/regtested on SPARC/Solaris, OK for mainline? Ok. Richard. > > 2017-01-10 Eric Botcazou <ebotcazou@adacore.com> > > PR rtl-optimization/79032 > * lra-constraints.c (simplify_operand_subreg): In the MEM case, test > the alignment of the adjusted memory reference against that of MODE, > instead of the alignment of the original memory reference. > > > 2017-01-10 Eric Botcazou <ebotcazou@adacore.com> > > * gcc.c-torture/execute/20170110-1.c: New test. > > -- > Eric Botcazou
Index: lra-constraints.c =================================================================== --- lra-constraints.c (revision 244194) +++ lra-constraints.c (working copy) @@ -1505,15 +1505,15 @@ simplify_operand_subreg (int nop, machin MEM_ADDR_SPACE (subst)))) { /* If we change the address for a paradoxical subreg of memory, the - address might violate the necessary alignment or the access might - be slow. So take this into consideration. We need not worry + new address might violate the necessary alignment or the access + might be slow; take this into consideration. We need not worry about accesses beyond allocated memory for paradoxical memory subregs as we don't substitute such equiv memory (see processing equivalences in function lra_constraints) and because for spilled pseudos we allocate stack memory enough for the biggest corresponding paradoxical subreg. */ - if (!(MEM_ALIGN (reg) < GET_MODE_ALIGNMENT (mode) - && SLOW_UNALIGNED_ACCESS (mode, MEM_ALIGN (reg))) + if (!(MEM_ALIGN (subst) < GET_MODE_ALIGNMENT (mode) + && SLOW_UNALIGNED_ACCESS (mode, MEM_ALIGN (subst))) || (MEM_ALIGN (reg) < GET_MODE_ALIGNMENT (innermode) && SLOW_UNALIGNED_ACCESS (innermode, MEM_ALIGN (reg)))) return true;