[gcc r14-10693] Fix small thinko in IPA mod/ref pass

[Eric Botcazou]

https://gcc.gnu.org/g:adab597af288d6e1e0b7c3414517147995b03cc9

commit r14-10693-gadab597af288d6e1e0b7c3414517147995b03cc9
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Fri Sep 20 12:32:13 2024 +0200

    Fix small thinko in IPA mod/ref pass
    
    When a memory copy operation is analyzed by analyze_ssa_name, if both the
    load and store are made through the same SSA name, the store is overlooked.
    
    gcc/
            * ipa-modref.cc (modref_eaf_analysis::analyze_ssa_name): Always
            process both the load and the store of a memory copy operation.
    
    gcc/testsuite/
            * gcc.dg/ipa/modref-4.c: New test.

Diff:
---
 gcc/ipa-modref.cc                   |  3 ++-
 gcc/testsuite/gcc.dg/ipa/modref-4.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/gcc/ipa-modref.cc b/gcc/ipa-modref.cc
index 10344fbb4b58..ccf788e6398c 100644
--- a/gcc/ipa-modref.cc
+++ b/gcc/ipa-modref.cc
@@ -2604,8 +2604,9 @@ modref_eaf_analysis::analyze_ssa_name (tree name, bool deferred)
 		 is used arbitrarily.  */
 	      if (memory_access_to (gimple_assign_rhs1 (assign), name))
 		m_lattice[index].merge (deref_flags (0, false));
+
 	      /* Handle *name = *exp.  */
-	      else if (memory_access_to (gimple_assign_lhs (assign), name))
+	      if (memory_access_to (gimple_assign_lhs (assign), name))
 		m_lattice[index].merge_direct_store ();
 	    }
 	  /* Handle lhs = *name.  */
diff --git a/gcc/testsuite/gcc.dg/ipa/modref-4.c b/gcc/testsuite/gcc.dg/ipa/modref-4.c
new file mode 100644
index 000000000000..71ed1ca5f5b6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/modref-4.c
@@ -0,0 +1,34 @@
+/* { dg-options "-O"  } */
+/* { dg-do run } */
+
+static __attribute__((noipa)) int foo (void)
+{
+  return 1;
+}
+
+int main (void)
+{
+  struct S { int a; int b; };
+  struct T { struct S s; };
+
+  struct T t = { { 0, 0 } };
+  struct T u;
+
+  __attribute__((noinline)) void bar (void)
+  {
+    if (foo ())
+      {
+	u = t;
+        /* OK with u.s.a = 0; */
+      }
+  }
+
+  u.s.a = 1;
+
+  bar ();
+
+  if (u.s.a != 0)
+    __builtin_abort ();
+
+  return 0;
+}