On Sat, Jun 13, 2009 at 9:29 AM, Alexandre Oliva<aol...@redhat.com> wrote: > So, after I tested and installed this patch > http://gcc.gnu.org/ml/gcc-patches/2009-06/msg00903.html I started > looking closely at the guality (debug info quality) test results. > > So far, I have only added two very simple tests to the guality > testsuite, but they already show very promising results. > > GUALCHKXPRVAL("expr", value, maybe_dead_p) checks whether expr, > evaluated by the debugger, matches value, evaluated at run time. > maybe_dead_p indicates whether, if the debugger fails to compute expr > (say, optimized away or missing debug info), we get an UNRESOLVED or a > FAIL. If expr is evaluated successfully but it doesn't match the > expected value, we get a FAIL, otherwise a PASS. > > GUALCHKXPR(expr) is the same as GUALCHKXPRVAL("expr",(expr),1) > > GUALCHKFLA(expr) is nearly equivalent to GUALCHKXPRVAL("expr",(expr),0), > except that (expr) is saved in a temporary and stored in a volatile > memory location after the check, so expr *must* be live at the point of > check. FLA stands for Forced Live After. > > Ok, on to some test results (on x86_64-linux-gnu): > > guality.c: > > int > main (int argc, char *argv[]) > { > int i = argc+1; > int j = argc-2; > int k = 5; > > GUALCHKXPR (argc); > GUALCHKXPR (i); > GUALCHKXPR (j); > GUALCHKXPR (k); > GUALCHKXPR (&i); > GUALCHKFLA (argc); > GUALCHKFLA (i); > GUALCHKFLA (j); > GUALCHKXPR (i); > GUALCHKXPR (j); > GUALCHKXPRVAL ("k", 5, 1); > GUALCHKXPRVAL ("0x40", 64, 0); > } > > -O0 (implied -fno-var-tracking-assignments) > > PASS: argc is 1 > PASS: i is 2 > FAIL: j is 32767, not -1 > FAIL: k is 2028276576, not 5 > PASS: &i is 140735221664248 > PASS: argc is 1 > PASS: i is 2 > FAIL: j is 32767, not -1 > PASS: i is 2 > FAIL: j is 32767, not -1 > FAIL: k is 2028276576, not 5 > PASS: 0x40 is 64 > FAIL: 7 PASS, 5 FAIL, 0 UNRESOLVED > > -O1 -fno-var-tracking-assignments > > PASS: argc is 1 > FAIL: i is 0, not 2 > PASS: j is -1 > UNRESOLVED: k is not computable, expected 5 > UNRESOLVED: &i is not computable, expected 140733781777644 > PASS: argc is 1 > PASS: i is 2 > PASS: j is -1 > FAIL: i is 0, not 2 > PASS: j is -1 > UNRESOLVED: k is not computable, expected 5 > PASS: 0x40 is 64 > FAIL: 7 PASS, 2 FAIL, 3 UNRESOLVED > > We see that debug info got better for j, and k is no longer wrong: it is > completely dropped from debug information, even though it could have > been encoded in standard debug info, for its value is the same constant > throughout its entire lifetime. For some reason, although i is > addressable, it's not uniformly computable: taking its address doesn't > work in between two sucessful evaluations of i, and &i actually works in > the debugger at those surrounding execution points. > > -O1 -fvar-tracking-assignments > > PASS: argc is 1 > UNRESOLVED: i is optimized away, expected 2 > PASS: j is -1 > UNRESOLVED: k is not computable, expected 5 > UNRESOLVED: &i is not computable, expected 140735863643740 > PASS: argc is 1 > PASS: i is 2 > PASS: j is -1 > UNRESOLVED: i is optimized away, expected 2 > PASS: j is -1 > UNRESOLVED: k is not computable, expected 5 > PASS: 0x40 is 64 > PASS: 7 PASS, 0 FAIL, 5 UNRESOLVED > > Yay, PASS! With Jakub's patch to encode constants in location lists, > the two UNRESOLVED tests for k will become PASS. I haven't looked into > why i is taken as optimized away. What I do know is that i isn't > tracked by VTA, for VTA only tracks variables that aren't addressable. > > Not convinced yet? Why, sure, VTA (+ DW_OP_implicit_value) has *only* > gone from totally broken j and k at -O0 to totally correct debug info, > while somehow *fixing* additional errors for i that is not even tracked > by VTA. From 0% to 100% correctness, and 100% completeness for all > VTA-tracked variables. > > But it gets better. > > Remember those examples from the slides in the VTA presentation in last > year's GCC Summit? http://people.redhat.com/~aoliva/papers/vta/ > > I've turned them into another guality test, that runs with GUALCHK(expr) > defined GUALCHKXPRVAL("expr", expr, 0), i.e., it requires variables to > be available and computable. > > typedef struct list { > struct list *n; > int v; > } elt, *node; > > node > find_val (node c, int v, node e) > { > while (c < e) > { > GUALCHK (c); > GUALCHK (v); > GUALCHK (e); > if (c->v == v) > return c; > GUALCHK (c); > GUALCHK (v); > GUALCHK (e); > c++; > } > return NULL; > } > > node > find_prev (node c, node w) > { > while (c) > { > node o = c; > c = c->n; > GUALCHK (c); > GUALCHK (o); > GUALCHK (w); > if (c == w) > return o; > GUALCHK (c); > GUALCHK (o); > GUALCHK (w); > } > return NULL; > } > > node > check_arr (node c, node e) > { > if (c == e) > return NULL; > e--; > while (c < e) > { > GUALCHK (c); > GUALCHK (e); > if (c->v > (c+1)->v) > return c; > GUALCHK (c); > GUALCHK (e); > c++; > } > return NULL; > } > > node > check_list (node c, node t) > { > while (c != t) > { > node n = c->n; > GUALCHK (c); > GUALCHK (n); > GUALCHK (t); > if (c->v > n->v) > return c; > GUALCHK (c); > GUALCHK (n); > GUALCHK (t); > c = n; > } > return NULL; > } > > struct list testme[] = { > { &testme[1], 2 }, > { &testme[2], 3 }, > { &testme[3], 5 }, > { &testme[4], 7 }, > { &testme[5], 11 }, > { NULL, 13 }, > }; > > int > main (int argc, char *argv[]) > { > int n = sizeof (testme) / sizeof (*testme); > node first, last, begin, end, ret; > > GUALCHKXPR (n); > > begin = first = &testme[0]; > last = &testme[n-1]; > end = &testme[n]; > > GUALCHKXPR (first); > GUALCHKXPR (last); > GUALCHKXPR (begin); > GUALCHKXPR (end); > > ret = find_val (begin, 13, end); > GUALCHK (ret); > assert (ret == last); > > ret = find_prev (first, last); > GUALCHK (ret); > assert (ret == &testme[n-2]); > > ret = check_arr (begin, end); > GUALCHK (ret); > assert (!ret); > > ret = check_list (first, last); > GUALCHK (ret); > assert (!ret); > } > > > -O0 (-fno-var-tracking-assignments implied) > > FAIL: n is 0, not 6 > FAIL: first is 16187408, not 6297888 > FAIL: last is 249832090421, not 6297968 > FAIL: begin is 140735655442656, not 6297888 > FAIL: end is 139872232800256, not 6297984 > PASS: c is 6297888 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297888 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297904 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297904 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297920 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297920 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297936 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297936 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297952 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297952 > PASS: v is 13 > PASS: e is 6297984 > PASS: c is 6297968 > PASS: v is 13 > PASS: e is 6297984 > FAIL: ret is 66, not 6297968 > PASS: c is 6297904 > FAIL: o is 55840872688, not 6297888 > PASS: w is 6297968 > PASS: c is 6297904 > FAIL: o is 55840872688, not 6297888 > PASS: w is 6297968 > PASS: c is 6297920 > FAIL: o is 55840872688, not 6297904 > PASS: w is 6297968 > PASS: c is 6297920 > FAIL: o is 55840872688, not 6297904 > PASS: w is 6297968 > PASS: c is 6297936 > FAIL: o is 55840872688, not 6297920 > PASS: w is 6297968 > PASS: c is 6297936 > FAIL: o is 55840872688, not 6297920 > PASS: w is 6297968 > PASS: c is 6297952 > FAIL: o is 55840872688, not 6297936 > PASS: w is 6297968 > PASS: c is 6297952 > FAIL: o is 55840872688, not 6297936 > PASS: w is 6297968 > PASS: c is 6297968 > FAIL: o is 55840872688, not 6297952 > PASS: w is 6297968 > FAIL: ret is 66, not 6297952 > PASS: c is 6297888 > PASS: e is 6297968 > PASS: c is 6297888 > PASS: e is 6297968 > PASS: c is 6297904 > PASS: e is 6297968 > PASS: c is 6297904 > PASS: e is 6297968 > PASS: c is 6297920 > PASS: e is 6297968 > PASS: c is 6297920 > PASS: e is 6297968 > PASS: c is 6297936 > PASS: e is 6297968 > PASS: c is 6297936 > PASS: e is 6297968 > PASS: c is 6297952 > PASS: e is 6297968 > PASS: c is 6297952 > PASS: e is 6297968 > FAIL: ret is 66, not 0 > PASS: c is 6297888 > FAIL: n is 6297968, not 6297904 > PASS: t is 6297968 > PASS: c is 6297888 > FAIL: n is 6297968, not 6297904 > PASS: t is 6297968 > PASS: c is 6297904 > FAIL: n is 6297968, not 6297920 > PASS: t is 6297968 > PASS: c is 6297904 > FAIL: n is 6297968, not 6297920 > PASS: t is 6297968 > PASS: c is 6297920 > FAIL: n is 6297968, not 6297936 > PASS: t is 6297968 > PASS: c is 6297920 > FAIL: n is 6297968, not 6297936 > PASS: t is 6297968 > PASS: c is 6297936 > FAIL: n is 6297968, not 6297952 > PASS: t is 6297968 > PASS: c is 6297936 > FAIL: n is 6297968, not 6297952 > PASS: t is 6297968 > PASS: c is 6297952 > PASS: n is 6297968 > PASS: t is 6297968 > PASS: c is 6297952 > PASS: n is 6297968 > PASS: t is 6297968 > FAIL: ret is 66, not 0 > FAIL: 93 PASS, 26 FAIL, 0 UNRESOLVED > > -O2 -fno-var-tracking-assignments: > > UNRESOLVED: n is not computable, expected 6 > UNRESOLVED: first is not computable, expected 6297408 > UNRESOLVED: last is not computable, expected 6297488 > UNRESOLVED: begin is not computable, expected 6297408 > UNRESOLVED: end is not computable, expected 6297504 > PASS: c is 6297408 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297408 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297424 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297424 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297440 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297440 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297456 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297456 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297472 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297472 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297488 > PASS: v is 13 > PASS: e is 6297504 > FAIL: ret is not computable, expected 6297488 > PASS: c is 6297424 > FAIL: o is optimized away, expected 6297408 > PASS: w is 6297488 > PASS: c is 6297424 > FAIL: o is optimized away, expected 6297408 > PASS: w is 6297488 > PASS: c is 6297440 > FAIL: o is optimized away, expected 6297424 > PASS: w is 6297488 > PASS: c is 6297440 > FAIL: o is optimized away, expected 6297424 > PASS: w is 6297488 > PASS: c is 6297456 > FAIL: o is optimized away, expected 6297440 > PASS: w is 6297488 > PASS: c is 6297456 > FAIL: o is optimized away, expected 6297440 > PASS: w is 6297488 > PASS: c is 6297472 > FAIL: o is optimized away, expected 6297456 > PASS: w is 6297488 > PASS: c is 6297472 > FAIL: o is optimized away, expected 6297456 > PASS: w is 6297488 > PASS: c is 6297488 > FAIL: o is optimized away, expected 6297472 > PASS: w is 6297488 > FAIL: ret is not computable, expected 6297472 > FAIL: c is 6297424, not 6297408 > PASS: e is 6297488 > FAIL: c is 6297424, not 6297408 > PASS: e is 6297488 > FAIL: c is 6297440, not 6297424 > PASS: e is 6297488 > FAIL: c is 6297440, not 6297424 > PASS: e is 6297488 > FAIL: c is 6297456, not 6297440 > PASS: e is 6297488 > FAIL: c is 6297456, not 6297440 > PASS: e is 6297488 > FAIL: c is 6297472, not 6297456 > PASS: e is 6297488 > FAIL: c is 6297472, not 6297456 > PASS: e is 6297488 > FAIL: c is 6297488, not 6297472 > PASS: e is 6297488 > FAIL: c is 6297488, not 6297472 > PASS: e is 6297488 > FAIL: ret is not computable, expected 0 > PASS: c is 6297408 > PASS: n is 6297424 > PASS: t is 6297488 > PASS: c is 6297408 > PASS: n is 6297424 > PASS: t is 6297488 > PASS: c is 6297424 > PASS: n is 6297440 > PASS: t is 6297488 > PASS: c is 6297424 > PASS: n is 6297440 > PASS: t is 6297488 > PASS: c is 6297440 > PASS: n is 6297456 > PASS: t is 6297488 > PASS: c is 6297440 > PASS: n is 6297456 > PASS: t is 6297488 > PASS: c is 6297456 > PASS: n is 6297472 > PASS: t is 6297488 > PASS: c is 6297456 > PASS: n is 6297472 > PASS: t is 6297488 > PASS: c is 6297472 > PASS: n is 6297488 > PASS: t is 6297488 > PASS: c is 6297472 > PASS: n is 6297488 > PASS: t is 6297488 > FAIL: ret is not computable, expected 0 > FAIL: 91 PASS, 23 FAIL, 5 UNRESOLVED > > Not much worse than -O0... Not only because some variables got > optimized away, but also because they got optimized in ways that I > “predicted” in the Summit, causing debug info to map to incorrect > locations. > > -O2 -fvar-tracking-assignments: > > UNRESOLVED: n is not computable, expected 6 > UNRESOLVED: first is not computable, expected 6297408 > UNRESOLVED: last is not computable, expected 6297488 > UNRESOLVED: begin is not computable, expected 6297408 > UNRESOLVED: end is not computable, expected 6297504 > PASS: c is 6297408 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297408 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297424 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297424 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297440 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297440 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297456 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297456 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297472 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297472 > PASS: v is 13 > PASS: e is 6297504 > PASS: c is 6297488 > PASS: v is 13 > PASS: e is 6297504 > FAIL: ret is 1, not 6297488 > PASS: c is 6297424 > PASS: o is 6297408 > PASS: w is 6297488 > PASS: c is 6297424 > PASS: o is 6297408 > PASS: w is 6297488 > PASS: c is 6297440 > PASS: o is 6297424 > PASS: w is 6297488 > PASS: c is 6297440 > PASS: o is 6297424 > PASS: w is 6297488 > PASS: c is 6297456 > PASS: o is 6297440 > PASS: w is 6297488 > PASS: c is 6297456 > PASS: o is 6297440 > PASS: w is 6297488 > PASS: c is 6297472 > PASS: o is 6297456 > PASS: w is 6297488 > PASS: c is 6297472 > PASS: o is 6297456 > PASS: w is 6297488 > PASS: c is 6297488 > PASS: o is 6297472 > PASS: w is 6297488 > FAIL: ret is 1, not 6297472 > PASS: c is 6297408 > PASS: e is 6297488 > PASS: c is 6297408 > PASS: e is 6297488 > PASS: c is 6297424 > PASS: e is 6297488 > PASS: c is 6297424 > PASS: e is 6297488 > PASS: c is 6297440 > PASS: e is 6297488 > PASS: c is 6297440 > PASS: e is 6297488 > PASS: c is 6297456 > PASS: e is 6297488 > PASS: c is 6297456 > PASS: e is 6297488 > PASS: c is 6297472 > PASS: e is 6297488 > PASS: c is 6297472 > PASS: e is 6297488 > FAIL: ret is 1, not 0 > PASS: c is 6297408 > PASS: n is 6297424 > PASS: t is 6297488 > PASS: c is 6297408 > PASS: n is 6297424 > PASS: t is 6297488 > PASS: c is 6297424 > PASS: n is 6297440 > PASS: t is 6297488 > PASS: c is 6297424 > PASS: n is 6297440 > PASS: t is 6297488 > PASS: c is 6297440 > PASS: n is 6297456 > PASS: t is 6297488 > PASS: c is 6297440 > PASS: n is 6297456 > PASS: t is 6297488 > PASS: c is 6297456 > PASS: n is 6297472 > PASS: t is 6297488 > PASS: c is 6297456 > PASS: n is 6297472 > PASS: t is 6297488 > PASS: c is 6297472 > PASS: n is 6297488 > PASS: t is 6297488 > PASS: c is 6297472 > PASS: n is 6297488 > PASS: t is 6297488 > FAIL: ret is 1, not 0 > FAIL: 110 PASS, 4 FAIL, 5 UNRESOLVED > > Pretty good, eh? And the 4 failures are easy to fix: ret is noted in > debug info as being held in a call-clobbered register at the time of the > call to the function that implements GUALCHK. It was saved in another > call-saved register, but the annotation that says so, right after the > call, only takes effect after the call. > > Although this could be fixed by changing the logic that emits debug info > before calls, so as to note the change in location earlier, this would > be wrong on two accounts: if you're at the pc of the call, you want to > be able to inspect the variable, and you want all locations in which > it's live, so that they can all be modified. > > So the proper fix would be to emit annotations right after the call that > take effect after we perform the call, but before it returns, i.e., > annotations at next_pc-1, rather than at next_pc. This would fix the > only 4 errors above. > > As for the UNRESOLVED bits, n would be fixed with DW_OP_implicit_value, > but the other four would require DW_OP_stack_value and some additional > fix in cfgexpand.c, to expand to (plus (symbol_ref) (const_int)) the > debug stmts that bind first, last, begin and end to &testme[<index>] at > the tree optimized dump. Then it would be another 100% pass rate, > without any UNRESOLVED whatsoever (all variables are tracked by VTA in > this testcase). > > Could it get any better?
Yes, I don't like -O0 producing worse debug info - what does the -O0 -fvar-tracking-assignments results look like? Richard. > -- > Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ > You must be the change you wish to see in the world. -- Gandhi > Be Free! -- http://FSFLA.org/ FSF Latin America board member > Free Software Evangelist Red Hat Brazil Compiler Engineer >
