[RFC] tree-optimization: fix optimize-out variables passed into func to alloc

[Alexey Lapshin <alexey.lapshin@espressif.com>]

After updating to GCC newer than 11.4.0 we found that some code started
to fail if it was built with size optimization (-Os).
You can find testsuite for reproduction in the attached patch.

The simplified version affected code looks like this:

void alloc_function (unsigned char **data_p) {
  *data_p = malloc (8);
  assert(*data_p != NULL);
}
int main () {
  int *data;
  alloc_function (&data);
  printf ("data pointer is %p", data); // prints NULL(compile with -Os)
}

If the type of passed argument is equal to the type in alloc_function
declaration it works perfectly. Also helps change one or both types to
void.

I found that issue started to appear from commit
d119f34c952f8718fdbabc63e2f369a16e92fa07
if-statement which leads to this issue was found and after being
removed seems it works well.

Could you please elaborate on what cases exactly this checking should
optimize?
I think it should also contain at least one more check for accessing
variable's memory to write..


---
 gcc/testsuite/gcc.dg/tree-ssa/alloc-in-func.c | 17 +++++++++++++++++
 gcc/tree-ssa-alias.cc                         |  2 --
 2 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/alloc-in-func.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alloc-in-func.c
b/gcc/testsuite/gcc.dg/tree-ssa/alloc-in-func.c
new file mode 100644
index 00000000000..b30c1cedcb9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/alloc-in-func.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+/* { dg-options "-Os" } */
+
+#define assert(x) if (!(x)) __builtin_abort ()
+
+static inline void alloc_function (unsigned char **data_p)
+{
+    *data_p = (unsigned char *) __builtin_malloc (10);
+    assert (*data_p != (void *)0);
+}
+
+int main ()
+{
+    int *data = (void *)0;
+    alloc_function ((unsigned char **) &data);
+    assert (data != (void *)0);
+}
diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
index b8f107dfa52..9068db300e5 100644
--- a/gcc/tree-ssa-alias.cc
+++ b/gcc/tree-ssa-alias.cc
@@ -2608,8 +2608,6 @@ modref_may_conflict (const gcall *stmt,
 	  if (num_tests >= max_tests)
 	    return true;
 	  alias_stats.modref_tests++;
-	  if (!alias_sets_conflict_p (base_set, base_node->base))
-	    continue;
 	  num_tests++;
 	}
 
-- 
2.34.1