[gcc r11-5773] jump: Also handle jumps wrapped in UNSPEC or UNSPEC_VOLATILE

[gcc r11-5773] jump: Also handle jumps wrapped in UNSPEC or UNSPEC_VOLATILE

[Maciej W. Rozycki]

https://gcc.gnu.org/g:630c9a4d54de7c084e146afe82c6e89a9f2cf3d7

commit r11-5773-g630c9a4d54de7c084e146afe82c6e89a9f2cf3d7
Author: Maciej W. Rozycki <macro@linux-mips.org>
Date:   Sat Dec 5 18:26:25 2020 +0000

    jump: Also handle jumps wrapped in UNSPEC or UNSPEC_VOLATILE
    
    VAX has interlocked branch instructions used for atomic operations and
    we want to have them wrapped in UNSPEC_VOLATILE so as not to have code
    carried across.  This however breaks with jump optimization and leads
    to an ICE in the build of libbacktrace like:
    
    .../libbacktrace/mmap.c:190:1: internal compiler error: in fixup_reorder_chain, at cfgrtl.c:3934
      190 | }
          | ^
    0x1087d46b fixup_reorder_chain
            .../gcc/cfgrtl.c:3934
    0x1087f29f cfg_layout_finalize()
            .../gcc/cfgrtl.c:4447
    0x1087c74f execute
            .../gcc/cfgrtl.c:3662
    
    on RTL like:
    
    (jump_insn 18 17 150 4 (unspec_volatile [
                (set (pc)
                    (if_then_else (eq (zero_extract:SI (mem/v:SI (reg/f:SI 23 [ _2 ]) [-1  S4 A32])
                                (const_int 1 [0x1])
                                (const_int 0 [0]))
                            (const_int 1 [0x1]))
                        (label_ref 20)
                        (pc)))
                (set (zero_extract:SI (mem/v:SI (reg/f:SI 23 [ _2 ]) [-1  S4 A32])
                        (const_int 1 [0x1])
                        (const_int 0 [0]))
                    (const_int 1 [0x1]))
            ] 101) ".../libbacktrace/mmap.c":135:14 158 {jbbssisi}
         (nil)
     -> 20)
    
    when those branches are enabled with a follow-up change.  Also showing
    with:
    
    FAIL: gcc.dg/pr61756.c (internal compiler error)
    
    Handle branches wrapped in UNSPEC_VOLATILE then and, for consistency,
    also in UNSPEC.  The presence of UNSPEC_VOLATILE will prevent such
    branches from being removed as they won't be accepted by `onlyjump_p',
    we just need to let them through.
    
            gcc/
            * jump.c (pc_set): Also accept a jump wrapped in UNSPEC or
            UNSPEC_VOLATILE.
            (any_uncondjump_p, any_condjump_p): Update comment accordingly.

Diff:
---
 gcc/jump.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/gcc/jump.c b/gcc/jump.c
index 34a8f209e20..c508467c696 100644
--- a/gcc/jump.c
+++ b/gcc/jump.c
@@ -850,9 +850,17 @@ pc_set (const rtx_insn *insn)
   pat = PATTERN (insn);
 
   /* The set is allowed to appear either as the insn pattern or
-     the first set in a PARALLEL.  */
-  if (GET_CODE (pat) == PARALLEL)
-    pat = XVECEXP (pat, 0, 0);
+     the first set in a PARALLEL, UNSPEC or UNSPEC_VOLATILE.  */
+  switch (GET_CODE (pat))
+    {
+    case PARALLEL:
+    case UNSPEC:
+    case UNSPEC_VOLATILE:
+      pat = XVECEXP (pat, 0, 0);
+      break;
+    default:
+      break;
+    }
   if (GET_CODE (pat) == SET && GET_CODE (SET_DEST (pat)) == PC)
     return pat;
 
@@ -860,7 +868,9 @@ pc_set (const rtx_insn *insn)
 }
 
 /* Return true when insn is an unconditional direct jump,
-   possibly bundled inside a PARALLEL.  */
+   possibly bundled inside a PARALLEL, UNSPEC or UNSPEC_VOLATILE.
+   The instruction may have various other effects so before removing the jump
+   you must verify onlyjump_p.  */
 
 int
 any_uncondjump_p (const rtx_insn *insn)
@@ -876,9 +886,9 @@ any_uncondjump_p (const rtx_insn *insn)
 }
 
 /* Return true when insn is a conditional jump.  This function works for
-   instructions containing PC sets in PARALLELs.  The instruction may have
-   various other effects so before removing the jump you must verify
-   onlyjump_p.
+   instructions containing PC sets in PARALLELs, UNSPECs or UNSPEC_VOLATILEs.
+   The instruction may have various other effects so before removing the jump
+   you must verify onlyjump_p.
 
    Note that unlike condjump_p it returns false for unconditional jumps.  */