gcc/ChangeLog:

PR middle-end/18628
* cse.c (fold_rtx_mem): Don't fold a load from a jumptable into a
register.
gcc/testsuite/ChangeLog:
* gcc.dg/pr18628.c: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@96445 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 910eb39..1e0a0f4 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,11 @@
 2005-03-14  Alexandre Oliva  <aoliva@redhat.com>
 
+       PR middle-end/18628
+       * cse.c (fold_rtx_mem): Don't fold a load from a jumptable into a
+       register.
+
+2005-03-14  Alexandre Oliva  <aoliva@redhat.com>
+
        PR c++/20280
        * gimplify.c (gimplify_cond_expr): Add fallback argument.  Use a
        temporary variable of pointer type if an lvalues is required.

diff --git a/gcc/cse.c b/gcc/cse.c
index d7f3027..fd5e21a 100644 (file)
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -3515,8 +3515,30 @@ fold_rtx_mem (rtx x, rtx insn)
            if (offset >= 0
                && (offset / GET_MODE_SIZE (GET_MODE (table))
                    < XVECLEN (table, 0)))
-             return XVECEXP (table, 0,
-                             offset / GET_MODE_SIZE (GET_MODE (table)));
+             {
+               rtx label = XVECEXP
+                 (table, 0, offset / GET_MODE_SIZE (GET_MODE (table)));
+               rtx set;
+
+               /* If we have an insn that loads the label from the
+                  jumptable into a reg, we don't want to set the reg
+                  to the label, because this may cause a reference to
+                  the label to remain after the label is removed in
+                  some very obscure cases (PR middle-end/18628).  */
+               if (!insn)
+                 return label;
+
+               set = single_set (insn);
+
+               if (! set || SET_SRC (set) != x)
+                 return x;
+
+               /* If it's a jump, it's safe to reference the label.  */
+               if (SET_DEST (set) == pc_rtx)
+                 return label;
+
+               return x;
+             }
          }
        if (table_insn && JUMP_P (table_insn)
            && GET_CODE (PATTERN (table_insn)) == ADDR_DIFF_VEC)

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4e18492..3053e82 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2005-03-14  Alexandre Oliva  <aoliva@redhat.com>
 
+       * gcc.dg/pr18628.c: New.
+
+2005-03-14  Alexandre Oliva  <aoliva@redhat.com>
+
        PR c++/20280
        * g++.dg/tree-ssa/pr20280.C: New.
 

diff --git a/gcc/testsuite/gcc.dg/pr18628.c b/gcc/testsuite/gcc.dg/pr18628.c
new file mode 100644 (file)
index 0000000..d365075
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr18628.c
@@ -0,0 +1,31 @@
+/* { dg-do link } */
+/* { dg-options "-O2" } */
+
+/* PR middle-end/18628 exposed a problem in which cse folded a load
+   from a jump table into the label that was the target of the branch.
+   Unfortunately, the indirect jump was moved to a different basic
+   block, and the LABEL_REF copied to the register wasn't enough to
+   keep the cfg from optimizing the otherwise-unused label away.  So
+   we ended up with a dangling reference to the label.  */
+
+int i;
+
+int main()
+{
+  for (;;)
+  {
+    switch (i)
+    {
+      case 0:
+      case 1:
+        return 1;
+
+      case 2:
+      case 3:
+        return 0;
+
+      case 5:
+        --i;
+    }
+  }
+}