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[PATCH] (v2) Fix PR 40445: C++ ICE when using __builtin_unreachable() as only statement in a function.
- From: David Daney <ddaney at caviumnetworks dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 25 Jun 2009 09:43:11 -0700
- Subject: [PATCH] (v2) Fix PR 40445: C++ ICE when using __builtin_unreachable() as only statement in a function.
The test case for this PR reveals two problems.
The first and the cause of the initial ICE is that get_last_bb_insn()
would return an insn from a different basic block if an empty block
followed the block in question. We would then ICE when rtl_delete_block
tried to delete an insn that was not part of the block.
To fix this issue, I create a new function, next_nonnote_insn_bb(), and
use it instead of next_nonnote_insn() in get_last_bb_insn().
Fixing that led to the case where all basic blocks and edges were being
removed. There are many places in the RTL optimizers that assume the
ENTRY_BLOCK will have a successor. With the test case, it did not.
The fix for this second problem is to revisit the patch that removes
empty blocks with no successors:
http://gcc.gnu.org/ml/gcc-patches/2009-06/msg00912.html
We refine the criteria a little and only remove such blocks that are not
the successor of the ENTRY_BLOCK.
As part of looking at all this, I also found that we were missing a
'continue' after removing empty fallthrough blocks. I added it so that
all the checks will be done for blocks following the removed empty
fallthrough block.
Tested by bootstrapping on x86_64-pc-linux-gnu all default languages
(both -m32 and -m64) with no regressions found.
OK to commit?
gcc/
2009-06-25 David Daney <ddaney@caviumnetworks.com>
PR rtl-optimization/40445
* emit-rtl.c (next_nonnote_insn_bb): New function.
* rtl.h (next_nonnote_insn_bb): Declare new function.
* cfgcleanup.c (try_optimize_cfg): Don't remove an empty block
with no successors that is the successor of the ENTRY_BLOCK.
Continue from the top after removing an empty fallthrough block.
* cfgrtl.c (get_last_bb_insn): Call next_nonnote_insn_bb instead
of next_nonnote_insn.
gcc/testsuite
2009-06-25 David Daney <ddaney@caviumnetworks.com>
PR rtl-optimization/40445
* g++.dg/other/builtin-unreachable-1.C: New testcase.
Index: gcc/testsuite/g++.dg/other/builtin-unreachable-1.C
===================================================================
--- gcc/testsuite/g++.dg/other/builtin-unreachable-1.C (revision 0)
+++ gcc/testsuite/g++.dg/other/builtin-unreachable-1.C (revision 0)
@@ -0,0 +1,11 @@
+// PR c++/40445
+// Check that a function containing only __builtin_unreachable()
+// doesn't ICE.
+
+// { dg-do compile }
+// { dg-options "-O0" }
+const char *
+f (void)
+{
+ __builtin_unreachable ();
+}
Index: gcc/emit-rtl.c
===================================================================
--- gcc/emit-rtl.c (revision 148867)
+++ gcc/emit-rtl.c (working copy)
@@ -3044,6 +3044,25 @@ next_nonnote_insn (rtx insn)
return insn;
}
+/* Return the next insn after INSN that is not a NOTE, but stop the
+ search before we enter another basic block. This routine does not
+ look inside SEQUENCEs. */
+
+rtx
+next_nonnote_insn_bb (rtx insn)
+{
+ while (insn)
+ {
+ insn = NEXT_INSN (insn);
+ if (insn == 0 || !NOTE_P (insn))
+ break;
+ if (NOTE_INSN_BASIC_BLOCK_P (insn))
+ return NULL_RTX;
+ }
+
+ return insn;
+}
+
/* Return the previous insn before INSN that is not a NOTE. This routine does
not look inside SEQUENCEs. */
Index: gcc/cfgcleanup.c
===================================================================
--- gcc/cfgcleanup.c (revision 148867)
+++ gcc/cfgcleanup.c (working copy)
@@ -1841,10 +1841,16 @@ try_optimize_cfg (int mode)
/* Delete trivially dead basic blocks. This is either
blocks with no predecessors, or empty blocks with no
- successors. Empty blocks may result from expanding
+ successors. However if the empty block with no
+ successors is the successor of the ENTRY_BLOCK, it is
+ kept. This ensures that the ENTRY_BLOCK will have a
+ successor which is a precondition for many RTL
+ passes. Empty blocks may result from expanding
__builtin_unreachable (). */
if (EDGE_COUNT (b->preds) == 0
- || (EDGE_COUNT (b->succs) == 0 && BB_HEAD (b) == BB_END (b)))
+ || (EDGE_COUNT (b->succs) == 0
+ && BB_HEAD (b) == BB_END (b)
+ && single_succ_edge (ENTRY_BLOCK_PTR)->dest != b))
{
c = b->prev_bb;
if (dump_file)
@@ -1916,6 +1922,7 @@ try_optimize_cfg (int mode)
delete_basic_block (b);
changed = true;
b = c;
+ continue;
}
if (single_succ_p (b)
Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h (revision 148867)
+++ gcc/rtl.h (working copy)
@@ -1626,6 +1626,7 @@ extern rtx previous_insn (rtx);
extern rtx next_insn (rtx);
extern rtx prev_nonnote_insn (rtx);
extern rtx next_nonnote_insn (rtx);
+extern rtx next_nonnote_insn_bb (rtx);
extern rtx prev_real_insn (rtx);
extern rtx next_real_insn (rtx);
extern rtx prev_active_insn (rtx);
Index: gcc/cfgrtl.c
===================================================================
--- gcc/cfgrtl.c (revision 148867)
+++ gcc/cfgrtl.c (working copy)
@@ -1712,11 +1712,11 @@ get_last_bb_insn (basic_block bb)
end = tmp;
/* Include any barriers that may follow the basic block. */
- tmp = next_nonnote_insn (end);
+ tmp = next_nonnote_insn_bb (end);
while (tmp && BARRIER_P (tmp))
{
end = tmp;
- tmp = next_nonnote_insn (end);
+ tmp = next_nonnote_insn_bb (end);
}
return end;