[Bug target/104894] [11/12 Regression] ICE with -fno-plt -mcpu=power10 on PowerPC64 LE Linux

["bergner at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104894

--- Comment #8 from Peter Bergner <bergner at gcc dot gnu.org> ---
Sorry for the delay, but getting back to this now...

(In reply to Alan Modra from comment #6)
> What I should have said is that -mlongcall code is correct but is
> missing a sibcall optimisation.  -fno-plt code (after removing the assert or
> using your patch) is incorrect.  A direct call is wrong, because it may
> require a plt call stub.  gcc ought to be producing an inline plt call. 

First off, is it just me, or does the -fno-plt option seem to slow down
basically all function calls since it forces us to emit a call that uses an
inline plt?  Even for functions that don't need it. 


> Change the testcase to
> 
> void foo();
> 
> void bar() {
>    foo();
>    foo();
> }
> 
> to see what I mean.  The asm output is
[snip]
> That "b foo@notoc" ought to be
>         pld 12,0(0),1
>         .reloc .-8,R_PPC64_PLT_PCREL34_NOTOC,foo
>         mtctr 12
>         .reloc .-4,R_PPC64_PLTSEQ,foo
>         .reloc .,R_PPC64_PLTCALL_NOTOC,foo
>         bctr

Thanks for the education!  The change below gives us that code sequence:

bar:
.LFB0:
        .cfi_startproc
        .localentry     bar,1
        mflr 0
        std 0,16(1)
        stdu 1,-96(1)
        .cfi_def_cfa_offset 96
        .cfi_offset 65, 16
        pld 12,0(0),1
        .reloc .-8,R_PPC64_PLT_PCREL34_NOTOC,foo
        mtctr 12
        .reloc .-4,R_PPC64_PLTSEQ,foo
        .reloc .,R_PPC64_PLTCALL_NOTOC,foo
        bctrl
        pld 12,0(0),1
        .reloc .-8,R_PPC64_PLT_PCREL34_NOTOC,foo
        addi 1,1,96
        .cfi_def_cfa_offset 0
        mtctr 12
        ld 0,16(1)
        mtlr 0
        .cfi_restore 65
        bctr

How does this look now?  I'll go ahead and regtest this.


diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index cb18db06a2d..e045657a2b0 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -25659,11 +25659,21 @@ rs6000_sibcall_aix (rtx value, rtx func_desc, rtx
tlsarg, rtx cookie)
   rtx r12 = NULL_RTX;
   rtx func_addr = func_desc;

-  gcc_assert (INTVAL (cookie) == 0);
-
   if (global_tlsarg)
     tlsarg = global_tlsarg;

+  /* Handle longcall attributes.  */
+  if ((INTVAL (cookie) & CALL_LONG) != 0
+      && GET_CODE (func_desc) == SYMBOL_REF)
+    {
+      /* Only PCREL can do a sibling call to a longcall function,
+        because we don't need to restore the TOC register.  */
+      gcc_assert (rs6000_pcrel_p ());
+      func_desc = rs6000_longcall_ref (func_desc, tlsarg);
+    }
+  else
+    gcc_assert (INTVAL (cookie) == 0);
+
   /* For ELFv2, r12 and CTR need to hold the function address
      for an indirect call.  */
   if (GET_CODE (func_desc) != SYMBOL_REF && DEFAULT_ABI == ABI_ELFv2)