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Fix mode-switching problem for SH SJLJ exceptions
- From: Richard Sandiford <richard at codesourcery dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Fri, 20 Jul 2007 12:39:03 +0100
- Subject: Fix mode-switching problem for SH SJLJ exceptions
Functions that return a value usually end with the sequence:
A: (clobber (reg H))
...
B: (set (reg H) (reg P))
...
C: (use (reg H))
where H is the hard return register and P is the pseudo register
to which return values are assigned.
mode-switching.c uses a specially-split exit block to enforce MODE_EXIT
(the mode required on exit from a function). The code that creates this
block -- create_pre_exit -- tries to find insn B and starts the new block
immediately before (or sometimes immediately after) it.
However, B can be deleted if P is never initialised. In this case,
create_pre_exit splits the block immediately before A instead.
The code only searches for A and B in the fallthrough predecessor
to the exit block; it assumes that P is never initialised if the
block contains neither A nor B.
In some cases B may be made up of several individual insns.
create_pre_exit therefore records the range of modified registers
and stops on the first SET that doesn't assign to part of H.
It then asserts that it has found a SET or CLOBBER for the
whole of H (except in some corner cases).
This shows up a problem on SJLJ targets, where the call to the SJLJ
unregister function is inserted between A and B. If B has been deleted,
the first SET we find may be setting up the argument to that call.
We then stop the search without having found either A or B, so the
assertion triggers.
At this point we have already searched past the call itself, and this
seems bogus. We are supposed to enforce MODE_EXIT _after_ the last call.
I therefore just treated searches that reach a call in the same way as
searches that reach the beginning of a block.
Bootstrapped & regression-tested on x86_64-linux-gnu. Also regression-tested
on sh-elf (multilibs {,-m2,-m3,-m4,-m4/-ml}) and sh-wrs-vxworks. OK to
install?
Richard
gcc/
* mode-switching.c (create_pre_exit): Don't search past calls.
Index: gcc/mode-switching.c
===================================================================
--- gcc/mode-switching.c (revision 126715)
+++ gcc/mode-switching.c (working copy)
@@ -246,6 +246,17 @@ create_pre_exit (int n_entities, int *en
if (INSN_P (return_copy))
{
+ /* When using SJLJ exceptions, the call to the
+ unregister function is inserted between the
+ clobber of the return value and the copy.
+ We do not want to split the block before this
+ or any other call; if we have not found the
+ copy yet, the copy must have been deleted. */
+ if (CALL_P (return_copy))
+ {
+ short_block = 1;
+ break;
+ }
return_copy_pat = PATTERN (return_copy);
switch (GET_CODE (return_copy_pat))
{