[gcc r11-3257] Fix assertion checking failure with tail call

[Eric Botcazou]

https://gcc.gnu.org/g:225a08220e444371ae4867b3e2ace275d30af3d3

commit r11-3257-g225a08220e444371ae4867b3e2ace275d30af3d3
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Thu Sep 17 12:58:02 2020 +0200

    Fix assertion checking failure with tail call
    
    gcc/ChangeLog:
            PR middle-end/97078
            * function.c (use_register_for_decl): Test cfun->tail_call_marked
            for a parameter here instead of...
            (assign_parm_setup_reg): ...here.
    
    gcc/testsuite/ChangeLog:
            * gcc.dg/pr97078.c: New test.

Diff:
---
 gcc/function.c                 | 10 +++++++---
 gcc/testsuite/gcc.dg/pr97078.c |  9 +++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/gcc/function.c b/gcc/function.c
index c4c9930d725..c6129593b9b 100644
--- a/gcc/function.c
+++ b/gcc/function.c
@@ -2237,6 +2237,11 @@ use_register_for_decl (const_tree decl)
   if (optimize)
     return true;
 
+  /* Thunks force a tail call even at -O0 so we need to avoid creating a
+     dangling reference in case the parameter is passed by reference.  */
+  if (TREE_CODE (decl) == PARM_DECL && cfun->tail_call_marked)
+    return true;
+
   if (!DECL_REGISTER (decl))
     return false;
 
@@ -3328,9 +3333,8 @@ assign_parm_setup_reg (struct assign_parm_data_all *all, tree parm,
      of the parameter instead.  */
   if (data->arg.pass_by_reference && TYPE_MODE (TREE_TYPE (parm)) != BLKmode)
     {
-      /* Use a stack slot for debugging purposes, except if a tail call is
-	 involved because this would create a dangling reference.  */
-      if (use_register_for_decl (parm) || cfun->tail_call_marked)
+      /* Use a stack slot for debugging purposes if possible.  */
+      if (use_register_for_decl (parm))
 	{
 	  parmreg = gen_reg_rtx (TYPE_MODE (TREE_TYPE (parm)));
 	  mark_user_reg (parmreg);
diff --git a/gcc/testsuite/gcc.dg/pr97078.c b/gcc/testsuite/gcc.dg/pr97078.c
new file mode 100644
index 00000000000..997d5fb8dd9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr97078.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ffloat-store" } */
+
+extern void foo (long double);
+
+void bar (long double d)
+{
+  foo (d);
+}