On Tue, Sep 19, 2017 at 09:21:50PM +0000, Segher Boessenkool wrote: > With the 32-bit SVR4 ABI we don't have a red zone, so we have to restore > the callee-saved registers before we restore the stack pointer. > > The previous fix for this PR failed in two ways, for huge frames: first, > we use a negative offset from r11 in that case, so the (mem:BLK 11) access > does no good; second, sched does not handle accesses to mem:BLK correctly > in this case (does not make dependencies). > > This patch fixes it by doing a store to (mem:BLK (scratch)) instead. > This means no unrelated (not to stack) loads/stores can be moved over the > stack restore either, but so be it.
I backported this to GCC 7 now. Segher > 2017-09-19 Segher Boessenkool <seg...@kernel.crashing.org> > > PR target/77687 > * config/rs6000/rs6000.md (stack_restore_tie): Store to a scratch > address instead of to r1 and r11. > > gcc/testsuite/ > PR target/77687 > * gcc.target/powerpc/pr77687.c: New testcase. > > > --- > gcc/config/rs6000/rs6000.md | 6 ++---- > gcc/testsuite/gcc.target/powerpc/pr77687.c | 20 ++++++++++++++++++++ > 2 files changed, 22 insertions(+), 4 deletions(-) > create mode 100644 gcc/testsuite/gcc.target/powerpc/pr77687.c > > diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md > index 7f17628..13ba743 100644 > --- a/gcc/config/rs6000/rs6000.md > +++ b/gcc/config/rs6000/rs6000.md > @@ -13161,14 +13161,12 @@ (define_insn "stack_tie" > > ; Some 32-bit ABIs do not have a red zone, so the stack deallocation has to > ; stay behind all restores from the stack, it cannot be reordered to before > -; one. See PR77687. This insn is an add or mr, and a stack_tie on the > -; operands of that. > +; one. See PR77687. This insn is an add or mr, and a memory clobber. > (define_insn "stack_restore_tie" > [(set (match_operand:SI 0 "gpc_reg_operand" "=r,r") > (plus:SI (match_operand:SI 1 "gpc_reg_operand" "r,r") > (match_operand:SI 2 "reg_or_cint_operand" "O,rI"))) > - (set (mem:BLK (match_dup 0)) (const_int 0)) > - (set (mem:BLK (match_dup 1)) (const_int 0))] > + (set (mem:BLK (scratch)) (const_int 0))] > "TARGET_32BIT" > "@ > mr %0,%1 > diff --git a/gcc/testsuite/gcc.target/powerpc/pr77687.c > b/gcc/testsuite/gcc.target/powerpc/pr77687.c > new file mode 100644 > index 0000000..95b27ae > --- /dev/null > +++ b/gcc/testsuite/gcc.target/powerpc/pr77687.c > @@ -0,0 +1,20 @@ > +/* { dg-options "-std=gnu99 -O2" } */ > +/* { dg-final { scan-assembler-not {\mmr r?1,r?11\M.*11.*\mblr\M} } } */ > + > +/* PR77687: We used to do stack accesses (via r11) after restoring r1. */ > + > +void g(int, char *); > +const char * dum = "hello"; > + > +void f(int x) > +{ > + char big[200000]; > + start: > + g(x, big); > + g(x, big); > + register void *p asm("r11") = &&start; > + asm("" : : "r"(p)); > + asm("" : : :"r28"); > + asm("" : : :"r29"); > + asm("" : : :"r30"); > +} > -- > 1.8.3.1