[PATCH, i386]: Fix PR68701: ICE with -ffixed-ebp

[Uros Bizjak]

Hello!

Attached patch fixes a compilation corner case, where -ffixed-ebp
option interferes with stack realignment requirements (the realignment
without -maccumulate-outgoing-args needs live %ebp).

The ICE can be worked around by adding -maccumulate-outgoing-args to
compile flags, and this is what the patch does, in addition to
emitting an informative warning.

2015-12-08  Uros Bizjak  <ubizjak@gmail.com>

    PR target/68701
    * config/i386/i386.c (ix86_option_override_internal): Enable
    -maccumulate-outgoing-args when %ebp is fixed due to stack
    realignment requirements.

testsuite/ChangeLog:

2015-12-08  Uros Bizjak  <ubizjak@gmail.com>

    PR target/68701
    * testsuite/gcc.target/i386/pr68701-1.c: New test.
    * testsuite/gcc.target/i386/pr68701-2.c: Ditto.

Patch was bootstrapped and regression tested on x86_64-linux-gnu
{,-m32}. Patch was committed to mainline SVN and will be backported to
all active branches in a couple of days.

Uros.
-------------- next part --------------
Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c	(revision 231413)
+++ config/i386/i386.c	(working copy)
@@ -5296,6 +5296,17 @@ ix86_option_override_internal (bool main_args_p,
       opts->x_target_flags |= MASK_ACCUMULATE_OUTGOING_ARGS;
     }
 
+  /* Stack realignment without -maccumulate-outgoing-args requires %ebp,
+     so enable -maccumulate-outgoing-args when %ebp is fixed.  */
+  if (fixed_regs[BP_REG]
+      && !(opts->x_target_flags & MASK_ACCUMULATE_OUTGOING_ARGS))
+    {
+      if (opts_set->x_target_flags & MASK_ACCUMULATE_OUTGOING_ARGS)
+	warning (0, "fixed ebp register requires %saccumulate-outgoing-args%s",
+		 prefix, suffix);
+      opts->x_target_flags |= MASK_ACCUMULATE_OUTGOING_ARGS;
+    }
+
   /* Figure out what ASM_GENERATE_INTERNAL_LABEL builds as a prefix.  */
   {
     char *p;
Index: testsuite/gcc.target/i386/pr68701-1.c
===================================================================
--- testsuite/gcc.target/i386/pr68701-1.c	(nonexistent)
+++ testsuite/gcc.target/i386/pr68701-1.c	(working copy)
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O -ffixed-ebp -mno-accumulate-outgoing-args" } */
+
+/* { dg-warning "fixed ebp register requires" "" { target *-*-* } 0 } */
+
+void foo (void);
+
+int
+main (int argc, char *argv[])
+{
+  foo ();
+  return argc - 1;
+}
Index: testsuite/gcc.target/i386/pr68701-2.c
===================================================================
--- testsuite/gcc.target/i386/pr68701-2.c	(nonexistent)
+++ testsuite/gcc.target/i386/pr68701-2.c	(working copy)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O -ffixed-ebp -mno-accumulate-outgoing-args -mstackrealign -msse" } */
+
+/* { dg-warning "fixed ebp register requires" "" { target *-*-* } 0 } */
+
+typedef float V __attribute__((vector_size(16)));
+
+void bar (V a)
+{
+  volatile V b = a;
+}