postreload: Fix autoinc handling in reload_cse_move2add [PR94516]

The following testcase shows two separate issues caused by the cselib
changes.
One is that through the cselib sp tracking improvements on
... r12 = rsp; rsp -= 8; push cst1; push cst2; push cst3; call
rsp += 32; rsp -= 8; push cst4; push cst5; push cst6; call
rsp += 32; rsp -= 8; push cst7; push cst8; push cst9; call
rsp += 32
reload_cse_simplify_set decides to optimize the rsp += 32 insns
into rsp = r12 because cselib figures that the r12 register holds the right
value.  From the pure cost perspective that seems like a win and on its own
at least for -Os that would be beneficial, except that there are those
rsp -= 8 stack adjustments after it, where rsp += 32; rsp -= 8; is optimized
into rsp += 24; by the csa pass, but rsp = r12; rsp -= 8 can't.  Dunno
what to do about this part, the PR has a hack in a comment.

Anyway, the following patch fixes the other part, which isn't a missed
optimization, but a wrong-code issue.  The problem is that the pushes of
constant are on x86 represented through PRE_MODIFY and while
move2add_note_store has some code to handle {PRE,POST}_{INC,DEC} without
REG_INC note, it doesn't handle {PRE,POST}_MODIFY (that would be enough
to fix this testcase).  But additionally it looks misplaced, because
move2add_note_store is only called on the rtxes that are stored into,
while RTX_AUTOINC can happen not just in those, but anywhere else in the
instruction (e.g. pop insn can have autoinc in the SET_SRC MEM).
REG_INC note seems to be required for any autoinc except for stack pointer
autoinc which doesn't have those notes, so this patch just handles
the sp autoinc after the REG_INC note handling loop.

2020-04-08  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/94516
	* postreload.c: Include rtl-iter.h.
	(reload_cse_move2add): Handle SP autoinc here by FOR_EACH_SUBRTX_VAR
	looking for all MEMs with RTX_AUTOINC operand.
	(move2add_note_store): Remove {PRE,POST}_{INC,DEC} handling.

	* gcc.dg/torture/pr94516.c: New test.

1 files changed, 16 insertions, 11 deletions

diff --git a/gcc/postreload.c b/gcc/postreload.c
index 7cd5c7fc55f..8849679ae0f 100644
--- a/gcc/postreload.c
+++ b/gcc/postreload.c
@@ -41,6 +41,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-pass.h"
 #include "dbgcnt.h"
 #include "function-abi.h"
+#include "rtl-iter.h"
 
 static int reload_cse_noop_set_p (rtx);
 static bool reload_cse_simplify (rtx_insn *, rtx);
@@ -2090,6 +2091,21 @@ reload_cse_move2add (rtx_insn *first)
 		}
 	    }
 	}
+
+      /* There are no REG_INC notes for SP autoinc.  */
+      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)
+		reg_mode[STACK_POINTER_REGNUM] = VOIDmode;
+	    }
+	}
+
       note_stores (insn, move2add_note_store, insn);
 
       /* If INSN is a conditional branch, we try to extract an
@@ -2144,17 +2160,6 @@ move2add_note_store (rtx dst, const_rtx set, void *data)
   unsigned int regno = 0;
   scalar_int_mode mode;
 
-  /* Some targets do argument pushes without adding REG_INC notes.  */
-
-  if (MEM_P (dst))
-    {
-      dst = XEXP (dst, 0);
-      if (GET_CODE (dst) == PRE_INC || GET_CODE (dst) == POST_INC
-	  || GET_CODE (dst) == PRE_DEC || GET_CODE (dst) == POST_DEC)
-	reg_mode[REGNO (XEXP (dst, 0))] = VOIDmode;
-      return;
-    }
-
   if (GET_CODE (dst) == SUBREG)
     regno = subreg_regno (dst);
   else if (REG_P (dst))