tree-ssa-dse: Fix up handling of lhs of internal calls [PR108657]

The r13-1778 PR106378 tree-ssa-dse change didn't just add special support
for IFN_LEN_STORE and IFN_MASK_STORE internal function calls as I believe
was intended, but given that the function was
if (is builtin) { ... }
else if (lhs present and non-SSA_NAME) { ... }
return false;
and it added a new
else if (is internal builtin) { ... }
in between the two, the last if used to be done before on all stmts
with non-SSA_NAME lhs except for calls to builtin functions, but newly
isn't done also for calls to internal functions.  In the testcase
the important internal function is .DEFERRED_INIT, which often has
non-SSA_NAME lhs, and the change resulted in them no longer being DSEd,
so a block with nothing in it left but var = .DEFERRED_INIT () and
var = {CLOBBER} was unrolled several times.

The following patch does the lhs handling for all stmts with non-SSA_NAME lhs
unless initialize_ao_ref_for_dse handled those specially already and
returned (which is the case for various mem* builtins which don't have
such lhs, for some cases of calloc which again is fine,and since r13-1778
also for IFN_LEN_STORE call and some IFN_MASK_STORE calls.
As IFN_MASK_STORE doesn't have a lhs, the break for the !may_def_ok case
doesn't seem to change anything, and because we've handled internal fns
that way in the past, I think it is the right thing to do that again.
That said, if it is inappropriate for some new ifn, I guess it could
be added to the switch and just return false; for it instead of break;.

2023-02-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108657
	* tree-ssa-dse.cc (initialize_ao_ref_for_dse): If lhs of stmt
	exists and is not a SSA_NAME, call ao_ref_init even if the stmt
	is a call to internal or builtin function.

	* gcc.dg/pr108657.c: New test.

diff --git a/gcc/testsuite/gcc.dg/pr108657.c b/gcc/testsuite/gcc.dg/pr108657.c
new file mode 100644 (file)
index 0000000..37d0b8e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108657.c
@@ -0,0 +1,31 @@
+/* PR tree-optimization/108657 */
+/* { dg-do run } */
+/* { dg-options "-O3 -ftrivial-auto-var-init=zero" } */
+
+int c, e, f;
+static int *d = &c;
+
+__attribute__((noipa)) void
+foo (void)
+{
+  if (c != 1)
+    __builtin_abort ();
+}
+
+int
+main ()
+{
+  for (c = 1; c >= 0; c--)
+    {
+      e = 0;
+      for (int j = 0; j <= 2; j++)
+       {
+         short k[1];
+         if (e)
+           break;
+         e ^= f;
+       }
+    }
+  *d = 1;
+  foo ();
+}

diff --git a/gcc/tree-ssa-dse.cc b/gcc/tree-ssa-dse.cc
index 46ab57d..4f8a44f 100644 (file)
--- a/gcc/tree-ssa-dse.cc
+++ b/gcc/tree-ssa-dse.cc
@@ -177,7 +177,7 @@ initialize_ao_ref_for_dse (gimple *stmt, ao_ref *write, bool may_def_ok = false)
        default:;
        }
     }
-  else if (tree lhs = gimple_get_lhs (stmt))
+  if (tree lhs = gimple_get_lhs (stmt))
     {
       if (TREE_CODE (lhs) != SSA_NAME)
        {