[gcc r12-1176] Tame fix for PR ipa/99122

[Eric Botcazou]

https://gcc.gnu.org/g:ad085ef5fb4142df2027f81ea03992fdafc6e2f6

commit r12-1176-gad085ef5fb4142df2027f81ea03992fdafc6e2f6
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Thu Jun 3 12:39:39 2021 +0200

    Tame fix for PR ipa/99122
    
    The return part has a major performance impact in Ada where variable-sized
    types are first-class citizens, but it turns out that it is not exercized
    in the testsuite yet, so back it out for now.
    
    gcc/
            PR ipa/99122
            * tree-inline.c (inline_forbidden_p): Remove test on return type.
    gcc/testsuite/
            * gnat.dg/inline22.adb: New test.

Diff:
---
 gcc/testsuite/gnat.dg/inline22.adb | 19 +++++++++++++++++++
 gcc/tree-inline.c                  | 15 ++++-----------
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/gcc/testsuite/gnat.dg/inline22.adb b/gcc/testsuite/gnat.dg/inline22.adb
new file mode 100644
index 00000000000..5812c2f04df
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/inline22.adb
@@ -0,0 +1,19 @@
+-- { dg-compile }
+
+procedure Inline22 (L, U : Integer) is
+
+  type Arr is array (Integer range L .. U) of Boolean;
+
+  function Get_Zero return Arr;
+  pragma Inline_Always (Get_Zero);
+
+  function Get_Zero return Arr is
+  begin
+    return (others => False);
+  end;
+
+  A : Arr;
+
+begin
+  A := Get_Zero;
+end;
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 5396131e176..05d1a253d5b 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -4025,17 +4025,10 @@ inline_forbidden_p (tree fndecl)
   wi.info = (void *) fndecl;
   wi.pset = &visited_nodes;
 
-  /* We cannot inline a function with a VLA typed argument or result since
-     we have no implementation materializing a variable of such type in
-     the caller.  */
-  if (COMPLETE_TYPE_P (TREE_TYPE (TREE_TYPE (fndecl)))
-      && !poly_int_tree_p (TYPE_SIZE (TREE_TYPE (TREE_TYPE (fndecl)))))
-    {
-      inline_forbidden_reason
-	= G_("function %q+F can never be inlined because "
-	     "it has a VLA return argument");
-      return true;
-    }
+  /* We cannot inline a function with a variable-sized parameter because we
+     cannot materialize a temporary of such a type in the caller if need be.
+     Note that the return case is not symmetrical because we can guarantee
+     that a temporary is not needed by means of CALL_EXPR_RETURN_SLOT_OPT.  */
   for (tree parm = DECL_ARGUMENTS (fndecl); parm; parm = DECL_CHAIN (parm))
     if (!poly_int_tree_p (DECL_SIZE (parm)))
       {