[Bug target/79430] [7/8 Regression] action of statement incorrectly optimised away

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79430

--- Comment #78 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Untested fix.  The problem is that autoinc/dec of stack_pointer_rtx doesn't use
REG_INC notes (various comments, e.g. in auto_inc_p or in auto-inc-dec.c seem
to suggest that stack_pointer_rtx is just special in this regard) and reg_set_p
used by modified_between_p etc. thus doesn't consider push/pop instructions as
affecting the stack pointer and memory based on that.
--- gcc/rtlanal.c.jj    2017-01-05 11:43:10.000000000 +0100
+++ gcc/rtlanal.c       2017-04-26 11:38:16.510940053 +0200
@@ -1221,6 +1221,24 @@ reg_set_p (const_rtx reg, const_rtx insn
                  || find_reg_fusage (insn, CLOBBER, reg)))))
     return true;

+  /* There are no REG_INC notes for SP autoinc.  */
+  if (reg == stack_pointer_rtx && INSN_P (insn))
+    {
+      subrtx_var_iterator::array_type array;
+      FOR_EACH_SUBRTX_VAR (iter, array, PATTERN (insn), NONCONST)
+       {
+         rtx mem = *iter;
+         if (mem
+             && MEM_P (mem)
+             && GET_RTX_CLASS (GET_CODE (XEXP (mem, 0))) == RTX_AUTOINC)
+           {
+             if (XEXP (XEXP (mem, 0), 0) == stack_pointer_rtx)
+               return true;
+             iter.skip_subrtxes ();
+           }
+       }
+    }
+
   return set_of (reg, insn) != NULL_RTX;
 }