Hi Kaz,

This patch fixes a case in sh.c:find_barrier(), triggered by a testcase
in glibc. The scanning starts from a GOT move instruction, records
itself in 'last_got', but does not find a second GOT move (to reset
last_got to NULL).

It finishes by trying to insert a new barrier in the insn stream, sees
last_got != NULL, and tries to insert at PREV_INSN(last_got), which goes
above the original start insn.

The caller, sh_reorg(), then gets the barrier scan target above the orig
insn, tries (in vain) to find it using a forward scan, and segfaults
when it goes past the insn stream...

The attached patch adds an additional equality check, plus some comment
updates. Cross-tested without regressions, is this okay for trunk?


2012-03-27  Chung-Lin Tang  <clt...@codesourcery.com>

        PR target/52667
        * config/sh/sh.c (find_barrier): Add equality check of last_got
        to avoid going above orig insn. Update comments.

Index: config/sh/sh.c
--- config/sh/sh.c      (revision 185837)
+++ config/sh/sh.c      (working copy)
@@ -4751,8 +4751,12 @@ find_barrier (int num_mova, rtx mova, rtx from)
       /* Don't emit a constant table int the middle of global pointer setting,
         since that that would move the addressing base GOT into another table. 
         We need the first mov instruction before the _GLOBAL_OFFSET_TABLE_
-        in the pool anyway, so just move up the whole constant pool.  */
-      if (last_got)
+        in the pool anyway, so just move up the whole constant pool.
+        However, avoid doing so when the last single GOT mov is the starting
+        insn itself. Going past above the start insn would create a negative
+        offset, causing errors.  */
+      if (last_got && last_got != orig)
         from = PREV_INSN (last_got);
       /* Don't insert the constant pool table at the position which

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