From 95f17e26112d8a0700e8a9912e2f4f48a24ba1ea Mon Sep 17 00:00:00 2001 From: Bill Schmidt Date: Wed, 19 Aug 2020 13:43:55 -0500 Subject: [PATCH] rs6000: Enable more sibcalls when TOC is not preserved 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 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. --- gcc/config/rs6000/rs6000-logue.c | 30 +++++++++---------- .../gcc.target/powerpc/pcrel-sibcall-1.c | 19 ++++++++---- 2 files changed, 28 insertions(+), 21 deletions(-) diff --git a/gcc/config/rs6000/rs6000-logue.c b/gcc/config/rs6000/rs6000-logue.c index 6aad1ff826a..5a2cb7fdf2c 100644 --- a/gcc/config/rs6000/rs6000-logue.c +++ b/gcc/config/rs6000/rs6000-logue.c @@ -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 diff --git a/gcc/testsuite/gcc.target/powerpc/pcrel-sibcall-1.c b/gcc/testsuite/gcc.target/powerpc/pcrel-sibcall-1.c index dfcf8183ccd..9197788f98f 100644 --- a/gcc/testsuite/gcc.target/powerpc/pcrel-sibcall-1.c +++ b/gcc/testsuite/gcc.target/powerpc/pcrel-sibcall-1.c @@ -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} } } */ -- 2.30.2