forwprop: Fix copy prop aggregates into return statements slightly [PR124099]

So a few more restrictions are needed here.
First we don't need to change if the return statement is already
a RESULT_DECL nor deference of the RESULT_DECL.
Second proping a global variable into the return is ok for the most
part except enumtls does not know how to expand that correctly and things
go down hill. So restrict to non global vars now.

Bootstrapped and tested on x86_64-linux-gnu.
Also tested the testcase with TLS turned off so enumtls ran.

	PR tree-optimization/124099

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (optimize_agr_copyprop_return): Don't do anything
	if the return is already result decl or a deference of result decl.
	Also reject non local var decls.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/tls-return-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>

diff --git a/gcc/testsuite/gcc.dg/torture/tls-return-1.c b/gcc/testsuite/gcc.dg/torture/tls-return-1.c
new file mode 100644 (file)
index 0000000..aa56e42
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/tls-return-1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+
+/* PR tree-optimization/124099 */ 
+
+struct s1 { int t[2];};
+__thread struct s1 t;
+struct s1 g()
+{ 
+  return t;
+}

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index c4fde7b4aae0b7605cd25065ae4f8b3694a93e6b..931c0798a813c9060334fcef30848e8792c06c53 100644 (file)
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -1734,11 +1734,22 @@ optimize_agr_copyprop_return (gimple *defstmt, greturn *use,
       || is_gimple_min_invariant (rvalue)
       || TYPE_VOLATILE (TREE_TYPE (rvalue)))
     return;
+
+  /* `return <retval>;` is already the best it could be.
+     Likewise `return *<retval>_N(D)`.  */
+  if (TREE_CODE (rvalue) == RESULT_DECL
+      || (TREE_CODE (rvalue) == MEM_REF
+         && TREE_CODE (TREE_OPERAND (rvalue, 0)) == SSA_NAME
+         && TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (rvalue, 0)))
+              == RESULT_DECL))
+    return;
   tree newsrc = new_src_based_on_copy (rvalue, dest, src);
   if (!newsrc)
     return;
-  /* Currently only support decls, could support VCEs too? */
-  if (!DECL_P (newsrc))
+  /* Currently only support non-global vars.
+     See PR 124099 on enumtls not supporting expanding for GIMPLE_RETURN.
+     FIXME: could support VCEs too?  */
+  if (!VAR_P (newsrc) || is_global_var (newsrc))
     return;
   if (dump_file && (dump_flags & TDF_DETAILS))
     {