Hi,
Here is a smaller case for bug #897 and a new patch based on Gang's
current work. Could a gatekeeper review it? Thank you very much.
A smaller case:
1 int g_1;
2 int* g_2;
3 int* func(int* p_1, short p_2) {
4 int **l_1;
5 const unsigned long l_2 = 0x2A1DFCF9L;
6 for ( ; ; p_2 = foo() ) {
7 int ***l_3 = &l_1;
8 (*l_3) = &g_2;
9 if (!l_2) {
10 // The following code is unreachable
11 if ((bar())) {
12 (*g_2) |= g_1;
13 (**l_1) |= (*p_1);
14 g_2 = &g_1;
15 }
16 }
17 }
18 }
in DCE phase, the unreachable code elimination runs at first and all
the statements in the if block is removed and set to NOT_LIVE. In the
later Dead store elimination phase, as Gang's explaination, we follow
the U-D chain of g_2, which is a global variable and has CHI on line
6(foo), 11(bar), 12 (*g_2) and a real dec in line 14. When we mark the
call of foo (line 6) to be LIVE, the CHI of g_2 is also LIVE and
following the U-D chain, the CHI's on bar() and (*g_2) is also marked
to LIVE. When marking (*g_2) to live, we also mark that BB to live.
But the BB is empty (all statements have been removed in earlier
phase) and the assertion occures.
Here is a new patch:
Index: osprey/be/opt/opt_dce.cxx
===================================================================
--- osprey/be/opt/opt_dce.cxx (revision 3855)
+++ osprey/be/opt/opt_dce.cxx (working copy)
@@ -2619,7 +2619,10 @@
// NOTE: May at some time always have a defining statement, so
// we could remove the check for a null defstmt
// (i.e., if live-in values get some dummy def stmt)
- if ( cr->Defstmt() != NULL && !cr->Defstmt()->Live_stmt() ) {
+ // if defining statement doesn't belong to any BB, it's been
+ // removed in early unreachable code elimination phase.
+ if ( cr->Defstmt() != NULL && !cr->Defstmt()->Live_stmt() &&
+ cr->Defstmt()->Bb() != NULL ) {
// if we're making this statement live just because it's
// associated with a chi, see if we can get rid of "i = i"
// assignments. This only happens when zero-version is
Index: osprey/be/opt/opt_bb.cxx
===================================================================
--- osprey/be/opt/opt_bb.cxx (revision 3855)
+++ osprey/be/opt/opt_bb.cxx (working copy)
@@ -734,6 +734,7 @@
_stmtlist.Remove(stmt);
- stmt->Reset_live_stmt(); // WHIRL SSA: mark stmt dead
+ stmt->Set_bb(NULL);
}
void
If the statement has been removed from the BB, we reset its BB to
NULL. In the later phase, if a statement's BB is NULL, which means the
statement has been removed and we don't need to mark it to live.
Reseting the bb of dead statement to NULL also helps preventing more
bugs when trying to traverse the BB.
--
Regards,
Lai Jian-Xin
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