[Bug rtl-optimization/101188] [postreload] Uses content of a clobbered register

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101188

--- Comment #10 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Created attachment 55189
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55189&action=edit
Proposed patch for postreload.cc so analysis is not bypassing "next" insn.

(In reply to Georg-Johann Lay from comment #9)
> postreload.cc::reload_cse_move2add() loops over all insns, and at some point
> it encounters
> 
> (insn 44 14 15 2 (set (reg/f:HI 14 r14 [58])
>         (reg/v/f:HI 16 r16 [orig:51 self ] [51])) "fail1.c":28:5 101
> {*movhi_split}
>      (nil))
> 
> During the analysis for that insn, it executes
> 
> 	  rtx_insn *next = next_nonnote_nondebug_insn (insn);
> 	  rtx set = NULL_RTX;
> 	  if (next)
> 	    set = single_set (next);
> 
> where next is
> 
> (insn 15 44 16 2 (parallel [
>             (set (reg/f:HI 14 r14 [58])
>                 (plus:HI (reg/f:HI 14 r14 [58])
>                     (const_int 68 [0x44])))
>             (clobber (reg:QI 31 r31))
>         ]) "fail1.c":28:5 175 {addhi3_clobber}
>      (nil))
> 
> Further down, it continues with success = 0:
> 
>       if (success)
> 	delete_insn (insn);
>       changed |= success;
>       insn = next;
>       [...]
>       continue;
> 
> The scan then continues with NEXT_INSN (insn), which is the insn AFTER insn
> 15, so the CLOBBER of QI:31 in insn 15 is bypassed, and note_stores or
> similar is never executed on insn 15.

A simple solution is to not "insn = next;" and just to pseudo-delete insn so
that NEXT_INSN (insn) works in the for loop:

diff --git a/gcc/postreload.cc b/gcc/postreload.cc
index fb392651e1b..388b8c0a506 100644
--- a/gcc/postreload.cc
+++ b/gcc/postreload.cc
@@ -2031,9 +2031,8 @@ reload_cse_move2add (rtx_insn *first)
                            }
                        }
                      if (success)
-                       delete_insn (insn);
+                       SET_INSN_DELETED (insn);
                      changed |= success;
-                     insn = next;
                      move2add_record_mode (reg);
                      reg_offset[regno]
                        = trunc_int_for_mode (added_offset + base_offset,