[PATCH, i386]: Fix PR 77991, ICE on x32 in plus_constant, at explow.c

[Uros Bizjak]

Hello!

We have to return Pmode RTX from legitimize_tls_address. There was a
path that returned DImode, when SImode was expected. Since the code
deals with various linker bugs, let's leave the generated sequence
as-is and just convert it to Pmode before return.

2016-10-18  Uros Bizjak  <ubiz...@gmail.com>

    PR target/77991
    * config/i386/i386.c (legitimize_tls_address)
    <case TLS_MODEL_INITIAL_EXEC>: For TARGET_64BIT || TARGET_ANY_GNU_TLS
    convert dest to Pmode if different than Pmode.

testsuite/ChangeLog:

2016-10-18  Uros Bizjak  <ubiz...@gmail.com>

    PR target/77991
    * gcc.target/i386/pr77991.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Patch was committed to mainline SVN and will be backported to other
release branches.

Uros.

Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c  (revision 241216)
+++ config/i386/i386.c  (working copy)
@@ -16357,7 +16357,9 @@ legitimize_tls_address (rtx x, enum tls_model mode
          base = get_thread_pointer (tp_mode,
                                     for_mov || !TARGET_TLS_DIRECT_SEG_REFS);
          off = force_reg (tp_mode, off);
-         return gen_rtx_PLUS (tp_mode, base, off);
+         dest = gen_rtx_PLUS (tp_mode, base, off);
+         if (tp_mode != Pmode)
+           dest = convert_to_mode (Pmode, dest, 1);
        }
       else
        {
Index: testsuite/gcc.target/i386/pr77991.c
===================================================================
--- testsuite/gcc.target/i386/pr77991.c (nonexistent)
+++ testsuite/gcc.target/i386/pr77991.c (working copy)
@@ -0,0 +1,19 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-require-effective-target maybe_x32 } */
+/* { dg-options "-O2 -mx32 -maddress-mode=short" } */
+
+struct rcu_reader_data
+{
+  unsigned ctr;
+  _Bool waiting;
+}
+
+extern __thread rcu_reader;
+
+void rcu_read_lock()
+{
+  struct rcu_reader_data *x = &rcu_reader;
+  _Bool val = 0;
+
+  __atomic_store(&x->waiting, &val, 0);
+}