[gcc r13-8636] rtlanal: Fix set_noop_p for volatile loads or stores [PR114768]

[Jakub Jelinek]

https://gcc.gnu.org/g:ab3b83afc149edda11fa3c7cbb3815606731003b

commit r13-8636-gab3b83afc149edda11fa3c7cbb3815606731003b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Apr 19 08:47:53 2024 +0200

    rtlanal: Fix set_noop_p for volatile loads or stores [PR114768]
    
    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.
    
    2024-04-19  Jakub Jelinek  <jakub@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.
    
    (cherry picked from commit 9f295847a9c32081bdd0fe908ffba58e830a24fb)

Diff:
---
 gcc/rtlanal.cc                  | 11 +++++++----
 gcc/testsuite/gcc.dg/pr114768.c | 10 ++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/gcc/rtlanal.cc b/gcc/rtlanal.cc
index 6b02428b735..7edb07a9b2c 100644
--- a/gcc/rtlanal.cc
+++ b/gcc/rtlanal.cc
@@ -1639,12 +1639,15 @@ set_noop_p (const_rtx set)
     return 1;
 
   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);
diff --git a/gcc/testsuite/gcc.dg/pr114768.c b/gcc/testsuite/gcc.dg/pr114768.c
new file mode 100644
index 00000000000..ffe3b368638
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr114768.c
@@ -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" } } */
+
+void
+foo (int *p)
+{
+  *p = *(volatile int *) p;
+}