[PATCH] rtlanal: Fix set_noop_p for volatile loads or stores [PR114768]

[Jakub Jelinek]

Hi!

On the following testcase, combine propagates the mem/v load into mem store
with the same address and then removes it, because noop_move_p says it is a
no-op move.  If it was the other way around, i.e. mem/v store and mem load,
or both would be mem/v, it would be kept.
The problem is that rtx_equal_p never checks any kind of flags on the rtxes
(and I think it would be quite dangerous to change it at this point), and
set_noop_p checks side_effects_p on just one of the operands, not both.
In the MEM <- MEM set, it only checks it on the destination, in
store to ZERO_EXTRACT only checks it on the source.

The following patch adds the missing side_effects_p checks.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2024-04-19  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/114768
        * rtlanal.cc (set_noop_p): Don't return true for MEM <- MEM
        sets if src has side-effects or for stores into ZERO_EXTRACT
        if ZERO_EXTRACT operand has side-effects.

        * gcc.dg/pr114768.c: New test.

--- gcc/rtlanal.cc.jj   2024-02-24 12:45:28.674249100 +0100
+++ gcc/rtlanal.cc      2024-04-18 15:09:55.199499083 +0200
@@ -1637,12 +1637,15 @@ set_noop_p (const_rtx set)
     return true;
 
   if (MEM_P (dst) && MEM_P (src))
-    return rtx_equal_p (dst, src) && !side_effects_p (dst);
+    return (rtx_equal_p (dst, src)
+           && !side_effects_p (dst)
+           && !side_effects_p (src));
 
   if (GET_CODE (dst) == ZERO_EXTRACT)
-    return rtx_equal_p (XEXP (dst, 0), src)
-          && !BITS_BIG_ENDIAN && XEXP (dst, 2) == const0_rtx
-          && !side_effects_p (src);
+    return (rtx_equal_p (XEXP (dst, 0), src)
+           && !BITS_BIG_ENDIAN && XEXP (dst, 2) == const0_rtx
+           && !side_effects_p (src)
+           && !side_effects_p (XEXP (dst, 0)));
 
   if (GET_CODE (dst) == STRICT_LOW_PART)
     dst = XEXP (dst, 0);
--- gcc/testsuite/gcc.dg/pr114768.c.jj  2024-04-18 15:37:49.139433678 +0200
+++ gcc/testsuite/gcc.dg/pr114768.c     2024-04-18 15:43:30.389730365 +0200
@@ -0,0 +1,10 @@
+/* PR rtl-optimization/114768 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-rtl-final" } */
+/* { dg-final { scan-rtl-dump "\\\(mem/v:" "final" { target { ! { nvptx*-*-* } 
} } } } */
+
+void
+foo (int *p)
+{
+  *p = *(volatile int *) p;
+}

        Jakub