On Wed, May 4, 2022 at 2:47 AM Palmer Dabbelt <pal...@rivosinc.com> wrote: > > This test was relying on undefined behavior, with -Wundef I get > > gcc/testsuite/gcc.dg/pr102892-1.c: In function 'main': > cc/testsuite/gcc.dg/pr102892-1.c:14:18: warning: 'a' is used > uninitialized [-Wuninitialized] > 14 | for (long a; a < 1; ++a) > | ~~^~~ > gcc/testsuite/gcc.dg/pr102892-1.c:14:13: note: 'a' was declared here > 14 | for (long a; a < 1; ++a) > | ^ > > gcc/testsuite/ChangeLog:
Please verify if the testcase then still reproduces the missed DCE before the fix. An alternative solution might be to make a initialized from a global variable. > * gcc.dg/pr102892-1.c (main): Avoid undefined behavior. > --- > The discussion on bug 102892 > <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102892> suggests this may > always have been a result of undefined behavior, but with these simple > changes the test passes for me. No idea why we're hitting this in > RISC-V (and SPARC) and not elsewhere, and I also haven't gone back and > checked the original fix to see if it was always just UB causing the > issue. Happy to look at this further, but one suggestion on bugzilla > was to just drop the test as invalid so I didn't want to chase something > that didn't matter. > --- > gcc/testsuite/gcc.dg/pr102892-1.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/gcc/testsuite/gcc.dg/pr102892-1.c > b/gcc/testsuite/gcc.dg/pr102892-1.c > index a9302b536df..b13f94d2a87 100644 > --- a/gcc/testsuite/gcc.dg/pr102892-1.c > +++ b/gcc/testsuite/gcc.dg/pr102892-1.c > @@ -11,7 +11,7 @@ int > main () > { > long c = 0; > - for (long a; a < 1; ++a) > + for (long a = 0; a < 2; ++a) > for (; c <= 1; c++) { > bar(); > if (1 == b[c][0]) > -- > 2.34.1 >
