I failed to mention that this has been bootstrapped and tested on
powerpc64le-unknown-linux-gnu, with no regressions. Is this ok for trunk?
Thanks,
Bill
On 8/19/20 9:40 AM, Bill Schmidt via Gcc-patches wrote:
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 <wschm...@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.
---
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} } } */
