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rs6000: Enable more sibcalls when TOC is not preserved

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A function compiled with the PC-relative addressing model does not
require r2 to contain a TOC pointer, and does not guarantee that r2
will be preserved for its caller.  Such a function can make sibcalls
without restriction based on TOC preservation rules.  However, a
caller that does preserve r2 cannot make a sibcall to a callee that
does not.

2020-08-19  Bill Schmidt  <wschmidt@linux.ibm.com>

gcc/
	* config/rs6000/rs6000-logue.c (rs6000_decl_ok_for_sibcall):
	Sibcalls are always legal when the caller doesn't preserve r2.

gcc/testsuite/
	* gcc.target/powerpc/pcrel-sibcall-1.c: Adjust.
This commit is contained in:
Bill Schmidt 2020-08-19 13:43:55 -05:00
parent 5abc821556
commit 95f17e2611
2 changed files with 28 additions and 21 deletions
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30
gcc/config/rs6000/rs6000-logue.c
View File

@ -1080,28 +1080,28 @@ rs6000_decl_ok_for_sibcall (tree decl)
if (DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2)
{
/* Under the AIX or ELFv2 ABIs we can't allow calls to non-local
functions, because the callee may have a different TOC pointer to
the caller and there's no way to ensure we restore the TOC when
/* A function compiled using the PC-relative addressing model does not
use a TOC pointer; nor is it guaranteed to preserve the value of
r2 for its caller's TOC. Such a function may make sibcalls to any
function, whether local or external, without restriction based on
TOC-save/restore rules. */
if (rs6000_pcrel_p (cfun))
return true;
/* Otherwise, under the AIX or ELFv2 ABIs we can't allow sibcalls
to non-local functions, because the callee may not preserve the
TOC pointer, and there's no way to ensure we restore the TOC when
we return. */
if (!decl || DECL_EXTERNAL (decl) || DECL_WEAK (decl)
|| !(*targetm.binds_local_p) (decl))
return false;
/* Similarly, if the caller preserves the TOC pointer and the callee
doesn't (or vice versa), proper TOC setup or restoration will be
missed. For example, suppose A, B, and C are in the same binary
and A -> B -> C. A and B preserve the TOC pointer but C does not,
and B -> C is eligible as a sibcall. A will call B through its
local entry point, so A will not restore its TOC itself. B calls
C with a sibcall, so it will not restore the TOC. C does not
preserve the TOC, so it may clobber r2 with impunity. Returning
from C will result in a corrupted TOC for A. */
else if (rs6000_fndecl_pcrel_p (decl) != rs6000_pcrel_p (cfun))
/* A local sibcall from a function that preserves the TOC pointer
to a function that does not is invalid for the same reason. */
if (rs6000_fndecl_pcrel_p (decl))
return false;
else
return true;
return true;
}
/* With the secure-plt SYSV ABI we can't make non-local calls when

19
gcc/testsuite/gcc.target/powerpc/pcrel-sibcall-1.c
View File

@ -3,10 +3,9 @@
/* { dg-require-effective-target powerpc_elfv2 } */
/* { dg-require-effective-target power10_ok } */
/* Test that potential sibcalls are not generated when the caller preserves the
TOC and the callee doesn't, or vice versa. At present, -mcpu=power10 does
not enable pc-relative mode. Enable it here explicitly until it is turned
on by default. */
/* Test that potential sibcalls are generated when the caller does not
preserve the TOC, even for external calls; and that sibcalls are not
generated when the caller preserves the TOC but the callee does not. */
#pragma GCC target ("cpu=power10,pcrel")
int x (void) __attribute__((noinline));
@ -39,12 +38,20 @@ int xx (void)
return 1;
}
extern int yy (void);
#pragma GCC target ("cpu=power10,pcrel")
int notoc_call (void)
int notoc_sibcall (void)
{
return xx ();
}
int extern_sibcall (void)
{
return yy ();
}
/* { dg-final { scan-assembler {\mb x@notoc\M} } } */
/* { dg-final { scan-assembler {\mbl y\M} } } */
/* { dg-final { scan-assembler {\mbl xx@notoc\M} } } */
/* { dg-final { scan-assembler {\mb xx@notoc\M} } } */
/* { dg-final { scan-assembler {\mb yy@notoc\M} } } */