http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56654
Bug #: 56654
Summary: uninit warning behaves erratically
Classification: Unclassified
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: rgue...@gcc.gnu.org
CC: xinlian...@gmail.com
For c-c++-common/uninit-17.c we currently expect the uninit use at:
static void bar(int a, int *ptr)
{
do
{
int b; /* { dg-message "declared" } */
if (b < 40) {
ptr[0] = b;
}
b += 1; /* { dg-warning "may be used uninitialized" } */
ptr++;
}
while (--a != 0);
}
where I would expect it at the if stmt. Now, when I exchange the late
DOM and the late VRP passes I instead get the warning two lines earlier
(inside the guarded BB). But there is no change in the IL:
> diff -u a/uninit-17.c.131t.uninit1 b/uninit-17.c.131t.uninit1
--- a/uninit-17.c.131t.uninit1 2013-03-18 14:27:16.677116283 +0100
+++ b/uninit-17.c.131t.uninit1 2013-03-18 14:26:58.956922876 +0100
@@ -3,7 +3,13 @@
[WORKLIST]: add to initial list: b_5 = PHI <b_13(D)(2), b_7(6)>
[CHECK]: examining phi: b_5 = PHI <b_13(D)(2), b_7(6)>
-[CHECK]: Found unguarded use: b_7 = b_5 + 1;
+
+Use in stmt *ptr_6 = b_5;
+is guarded by :
+if (b_5 <= 39)
+
+[CHECK] Found def edge 1 in b_5 = PHI <b_13(D)(2), b_7(6)>
+[CHECK]: Found unguarded use: *ptr_6 = b_5;
void foobar(int, int*) (int a, int * ptr)
{
int b;
the only difference is in the order of b_5 immediate uses.
That is, find_uninit_use should impose an ordering when walking over
immediate uses - for example visit the most dominating use first.
