[Bug c/95141] [8/9/10/11 Regression] Incorrect integer overflow warning message for bitand expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141 --- Comment #4 from CVS Commits --- The master branch has been updated by Richard Biener : https://gcc.gnu.org/g:4a88caf21a0a85129f6c985ca13ba3eb54ff5366 commit r11-509-g4a88caf21a0a85129f6c985ca13ba3eb54ff5366 Author: Richard Biener Date: Tue May 19 07:58:33 2020 +0200 c/95141 - fix bogus integer overflow warning This fixes an integer overflow warning that ultimatively happens because of TREE_OVERFLOW propagating through transforms and the existing guard against this, 375 if (TREE_OVERFLOW_P (ret) 376 && !TREE_OVERFLOW_P (op0) 377 && !TREE_OVERFLOW_P (op1)) 378 overflow_warning (EXPR_LOC_OR_LOC (expr, input_location, being insufficient. Rather than trying to use sth like walk_tree to exhaustively walk operands (with the possibility of introducing quadraticness when folding larger expressions recursively) the following amends the above with an ad-hoc test for a binary op0 with a possibly constant op1. 2020-05-30 Richard Biener PR c/95141 gcc/c * c-fold.c (c_fully_fold_internal): Enhance guard on overflow_warning. gcc/testsuite * gcc.dg/pr95141.c: New testcase.
[Bug c/95141] [8/9/10/11 Regression] Incorrect integer overflow warning message for bitand expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141 --- Comment #3 from Richard Biener --- (In reply to Richard Biener from comment #2) > So there's already (OVF) at > > ((long unsigned int) IA1 & 158(OVF)) & 1 > > but we only check > > 375 if (TREE_OVERFLOW_P (ret) > 376 && !TREE_OVERFLOW_P (op0) > 377 && !TREE_OVERFLOW_P (op1)) > 378 overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), > ret, expr); > > which doesn't catch the pre-existing overflow on op0 which then propagates. > > The original overflow is introduced folding short 158 to signed char -98(OVF) > via convert.c:do_narrow: > > 437 /* We should do away with all this once we have a proper > 438 type promotion/demotion pass, see PR45397. */ > 439 expr = maybe_fold_build2_loc (dofold, loc, ex_form, typex, > 440 convert (typex, arg0), > 441 convert (typex, arg1)); > > specifically the convert (typex, arg1). > > Now TREE_OVERFLOW in general is quite a fragile thing, but it's tempting to > adjust the overflow_warning guard for this case ... > > The do_narrow code also specifically looks for overflow cases that matter > and does not perform narrowing then so clearing TREE_OVERFLOW there would > also look reasonable. > > Thus like the following? Should be cheaper than adding walk_tree to the > diagnostic guard. > > diff --git a/gcc/convert.c b/gcc/convert.c > index 42509c518a9..ed00ded1a89 100644 > --- a/gcc/convert.c > +++ b/gcc/convert.c > @@ -436,9 +436,16 @@ do_narrow (location_t loc, > } >/* We should do away with all this once we have a proper > type promotion/demotion pass, see PR45397. */ > + /* Above we checked for all cases where overflow matters, avoid > +geneating overflowed constants here which otherwise propagate > +and cause spurious warnings, see PR95141. */ > + tree converted_arg1 = convert (typex, arg1); > + if (TREE_OVERFLOW_P (converted_arg1) > + && !TREE_OVERFLOW_P (arg1)) > + converted_arg1 = drop_tree_overflow (converted_arg1); >expr = maybe_fold_build2_loc (dofold, loc, ex_form, typex, > convert (typex, arg0), > - convert (typex, arg1)); > + converted_arg1); >return convert (type, expr); > } Regresses FAIL: gcc.dg/overflow-warn-5.c (test for warnings, line 6) which looks like a useful warning to preserve. Lame "walk-tree" variant catching this case: diff --git a/gcc/c/c-fold.c b/gcc/c/c-fold.c index 63becfeaf2c..bd21d247051 100644 --- a/gcc/c/c-fold.c +++ b/gcc/c/c-fold.c @@ -374,6 +374,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands, ret = fold (expr); if (TREE_OVERFLOW_P (ret) && !TREE_OVERFLOW_P (op0) + && !(BINARY_CLASS_P (op0) && TREE_OVERFLOW_P (TREE_OPERAND (op0, 1))) && !TREE_OVERFLOW_P (op1)) overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), ret, expr); if (code == LSHIFT_EXPR
[Bug c/95141] [8/9/10/11 Regression] Incorrect integer overflow warning message for bitand expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141 Richard Biener changed: What|Removed |Added Status|NEW |ASSIGNED Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org --- Comment #2 from Richard Biener --- So there's already (OVF) at ((long unsigned int) IA1 & 158(OVF)) & 1 but we only check 375 if (TREE_OVERFLOW_P (ret) 376 && !TREE_OVERFLOW_P (op0) 377 && !TREE_OVERFLOW_P (op1)) 378 overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), ret, expr); which doesn't catch the pre-existing overflow on op0 which then propagates. The original overflow is introduced folding short 158 to signed char -98(OVF) via convert.c:do_narrow: 437 /* We should do away with all this once we have a proper 438 type promotion/demotion pass, see PR45397. */ 439 expr = maybe_fold_build2_loc (dofold, loc, ex_form, typex, 440 convert (typex, arg0), 441 convert (typex, arg1)); specifically the convert (typex, arg1). Now TREE_OVERFLOW in general is quite a fragile thing, but it's tempting to adjust the overflow_warning guard for this case ... The do_narrow code also specifically looks for overflow cases that matter and does not perform narrowing then so clearing TREE_OVERFLOW there would also look reasonable. Thus like the following? Should be cheaper than adding walk_tree to the diagnostic guard. diff --git a/gcc/convert.c b/gcc/convert.c index 42509c518a9..ed00ded1a89 100644 --- a/gcc/convert.c +++ b/gcc/convert.c @@ -436,9 +436,16 @@ do_narrow (location_t loc, } /* We should do away with all this once we have a proper type promotion/demotion pass, see PR45397. */ + /* Above we checked for all cases where overflow matters, avoid +geneating overflowed constants here which otherwise propagate +and cause spurious warnings, see PR95141. */ + tree converted_arg1 = convert (typex, arg1); + if (TREE_OVERFLOW_P (converted_arg1) + && !TREE_OVERFLOW_P (arg1)) + converted_arg1 = drop_tree_overflow (converted_arg1); expr = maybe_fold_build2_loc (dofold, loc, ex_form, typex, convert (typex, arg0), - convert (typex, arg1)); + converted_arg1); return convert (type, expr); }
[Bug c/95141] [8/9/10/11 Regression] Incorrect integer overflow warning message for bitand expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141 Jakub Jelinek changed: What|Removed |Added CC||jakub at gcc dot gnu.org Last reconfirmed||2020-05-15 Target Milestone|--- |8.5 Ever confirmed|0 |1 Summary|Incorrect integer overflow |[8/9/10/11 Regression] |warning message for bitand |Incorrect integer overflow |expression |warning message for bitand ||expression Status|UNCONFIRMED |NEW --- Comment #1 from Jakub Jelinek --- Started with r7-7544-g2d143ba8cfef7ef480c639882fd5518b7afd822b
