On 6/28/23 3:07 AM, Kewen.Lin wrote:
> I think the reason why we need to check common_deferred_options is at this
> time
> we can't distinguish the fixed_regs[2] is from the initialization or command
> line
> user explicit specification. But could we just update the FIXED_REGISTERS
> without
> FIXED_R2 and set FIXED_R2 when it's needed in this function instead? Then I'd
> expect that when we find fixed_regs[2] is set at the beginning of this
> function, it
> would mean users specify it explicitly and then we don't need this option
> checking?
Correct, rs6000_conditional_register_usage() is called after the handling of the
-ffixed-* options, so looking at fixed_regs[2] cannot tell us whether the user
used the -ffixed-r2 option or not if we initialize the FIXED_REGISTERS[2] slot
to 1. I think we went this route for two reasons:
1) We don't have to worry about anyone in the future adding more uses of
FIXED_REGISTERS and needing to update the value depending on ABI, options,
etc.
2) The options in common_deferred_options are "rare" options, so the common
case is that common_deferred_options will be NULL and we'll never drop
into that section.
I believe the untested patch below should also work, without having to scan
the (uncommonly used) options. Jeevitha, can you bootstrap and regtest the
patch below?
> Besides, IMHO we need a corresponding test case to cover this -ffixed-r2
> handling.
Good idea. I think we can duplicate the pr110320_2.c test case, replacing the
-mno-pcrel option with -ffixed-r2. Jeevitha, can you give that a try?
>> +/* { dg-require-effective-target power10_ok } */
>> +/* { dg-require-effective-target powerpc_pcrel } */
>
> Do we have some environment combination which supports powerpc_pcrel but not
> power10_ok? I'd expect that only powerpc_pcrel is enough.
I think I agree testing for powerpc_pcrel should be enough.
Peter
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index d197c3f3289..7c356a73ac6 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -10160,9 +10160,13 @@ rs6000_conditional_register_usage (void)
for (i = 32; i < 64; i++)
fixed_regs[i] = call_used_regs[i] = 1;
+ /* For non PC-relative code, GPR2 is unavailable for register allocation. */
+ if (FIXED_R2 && !rs6000_pcrel_p ())
+ fixed_regs[2] = 1;
+
/* The TOC register is not killed across calls in a way that is
visible to the compiler. */
- if (DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2)
+ if (fixed_regs[2] && (DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2))
call_used_regs[2] = 0;
if (DEFAULT_ABI == ABI_V4 && flag_pic == 2)
diff --git a/gcc/config/rs6000/rs6000.h b/gcc/config/rs6000/rs6000.h
index 3503614efbd..2a24fbdf9fd 100644
--- a/gcc/config/rs6000/rs6000.h
+++ b/gcc/config/rs6000/rs6000.h
@@ -812,7 +812,7 @@ enum data_align { align_abi, align_opt, align_both };
#define FIXED_REGISTERS \
{/* GPRs */ \
- 0, 1, FIXED_R2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, FIXED_R13, 0, 0, \
+ 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, FIXED_R13, 0, 0, \
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
/* FPRs */ \
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
