Two fixes for -fsplit-stack on powerpc64. I goofed on the block
scanned for uses of r12. ENTRY_BLOCK_PTR_FOR_FN is the fake one. The
next block is the first one having insns.
The second change emits an error if people use a global register
variable r29 with -fsplit-stack. For example:
register struct important_stuff *quick_access __asm__ ("r29");
Such code does exist in the wild, but probably doesn't currently use
-fsplit-stack.
The problem is that r29 is saved by morestack then used to pass the
old stack pointer to the normal function prologue. So on entry to a
function, r29 will be modified. It would be possible to restore r29
from the morestack frame in order to let the function body see the
original r29, I wrote such a patch, but that trick isn't safe if
someone is using r29 in a signal handler.
I suppose we could restore r29 and downgrade the error to a warning
that using a global register asm r29 isn't safe in signal handlers
with -fsplit-stack. What do you think, David?
* config/rs6000/rs6000.c (split_stack_arg_pointer_used_p): Scan
correct block for use of r12.
(rs6000_expand_split_stack_prologue): Error on r29 asm global reg.
Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c (revision 223857)
+++ gcc/config/rs6000/rs6000.c (working copy)
@@ -23450,7 +23450,7 @@ split_stack_arg_pointer_used_p (void)
/* Unfortunately we also need to do some code scanning, since
r12 may have been substituted for the pseudo. */
rtx_insn *insn;
- basic_block bb = ENTRY_BLOCK_PTR_FOR_FN (cfun);
+ basic_block bb = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb;
FOR_BB_INSNS (bb, insn)
if (NONDEBUG_INSN_P (insn))
{
@@ -25942,6 +25942,13 @@ rs6000_expand_split_stack_prologue (void)
if (!info->push_p)
return;
+ if (global_regs[29])
+ {
+ error ("-fsplit-stack uses register r29");
+ inform (DECL_SOURCE_LOCATION (global_regs_decl[29]),
+ "conflicts with %qD", global_regs_decl[29]);
+ }
+
allocate = info->total_size;
if (allocate > (unsigned HOST_WIDE_INT) 1 << 31)
{
--
Alan Modra
Australia Development Lab, IBM
