| Message ID | alpine.DEB.2.21.1911202315130.8373@digraph.polyomino.org.uk |
|---|---|
| State | New |
| Headers | show |
| Series | Make more bad uses of fallthrough attribute into pedwarns | expand |
On Wed, Nov 20, 2019 at 11:15:56PM +0000, Joseph Myers wrote: > Various bad uses of the [[fallthrough]] attribute are constraint > violations in C2x, so need pedwarns rather than warnings. > > This patch duly turns the relevant warnings into pedwarns. The > relevant code is not specific to C, and does not know which form the > attribute was given in ([[fallthrough]] or [[gnu::fallthrough]] or > __attribute__((fallthrough))), but as I understand it these usages are > also erroneous for C++ and it seems reasonable to give a pedwarn here > even when a form other than [[fallthrough]] is being used. > > The precise meaning of the standard wording about "The next statement > that would be executed" seems a but unclear in some corner cases; the > tests added keep to cases where it is clear whether or not the next > statement executed is of the required form. > > Bootstrapped with no regressions for x86_64-pc-linux-gnu. OK to commit > (the gimplify.c changes)? Can't approve but as the author of the code in question, I think this is OK. -- Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
On 11/20/19 4:15 PM, Joseph Myers wrote: > Various bad uses of the [[fallthrough]] attribute are constraint > violations in C2x, so need pedwarns rather than warnings. > > This patch duly turns the relevant warnings into pedwarns. The > relevant code is not specific to C, and does not know which form the > attribute was given in ([[fallthrough]] or [[gnu::fallthrough]] or > __attribute__((fallthrough))), but as I understand it these usages are > also erroneous for C++ and it seems reasonable to give a pedwarn here > even when a form other than [[fallthrough]] is being used. > > The precise meaning of the standard wording about "The next statement > that would be executed" seems a but unclear in some corner cases; the > tests added keep to cases where it is clear whether or not the next > statement executed is of the required form. > > Bootstrapped with no regressions for x86_64-pc-linux-gnu. OK to commit > (the gimplify.c changes)? > > gcc: > 2019-11-20 Joseph Myers <joseph@codesourcery.com> > > * gimplify.c (expand_FALLTHROUGH_r, expand_FALLTHROUGH): Use > pedwarn instead of warning_at for fallthrough not preceding a case > or default label. > > gcc/c-family: > 2019-11-20 Joseph Myers <joseph@codesourcery.com> > > * c-attribs.c (handle_fallthrough_attribute): Use pedwarn instead > of warning. > > gcc/testsuite: > 2019-11-20 Joseph Myers <joseph@codesourcery.com> > > * gcc.dg/c2x-attr-fallthrough-6.c: New test. Split out from > c2x-attr-fallthrough-3.c. > * gcc.dg/c2x-attr-fallthrough-1.c: Add more tests. > * gcc.dg/c2x-attr-fallthrough-2.c: Update expected diagnostics. > * gcc.dg/c2x-attr-fallthrough-3.c: Split inside-switch part of > test out to c2x-attr-fallthrough-6.c. OK jeff
Index: gcc/c-family/c-attribs.c =================================================================== --- gcc/c-family/c-attribs.c (revision 278510) +++ gcc/c-family/c-attribs.c (working copy) @@ -4117,7 +4117,7 @@ tree handle_fallthrough_attribute (tree *, tree name, tree, int, bool *no_add_attrs) { - warning (OPT_Wattributes, "%qE attribute ignored", name); + pedwarn (input_location, OPT_Wattributes, "%qE attribute ignored", name); *no_add_attrs = true; return NULL_TREE; } Index: gcc/gimplify.c =================================================================== --- gcc/gimplify.c (revision 278510) +++ gcc/gimplify.c (working copy) @@ -2405,8 +2405,8 @@ expand_FALLTHROUGH_r (gimple_stmt_iterator *gsi_p, gsi_next (&gsi2); } if (!found) - warning_at (loc, 0, "attribute %<fallthrough%> not preceding " - "a case label or default label"); + pedwarn (loc, 0, "attribute %<fallthrough%> not preceding " + "a case label or default label"); } break; default: @@ -2428,8 +2428,8 @@ expand_FALLTHROUGH (gimple_seq *seq_p) if (wi.callback_result == integer_zero_node) /* We've found [[fallthrough]]; at the end of a switch, which the C++ standard says is ill-formed; see [dcl.attr.fallthrough]. */ - warning_at (loc, 0, "attribute %<fallthrough%> not preceding " - "a case label or default label"); + pedwarn (loc, 0, "attribute %<fallthrough%> not preceding " + "a case label or default label"); } Index: gcc/testsuite/gcc.dg/c2x-attr-fallthrough-1.c =================================================================== --- gcc/testsuite/gcc.dg/c2x-attr-fallthrough-1.c (revision 278510) +++ gcc/testsuite/gcc.dg/c2x-attr-fallthrough-1.c (working copy) @@ -3,7 +3,7 @@ /* { dg-options "-std=c2x -pedantic-errors -Wextra" } */ int -f (int a) +f (int a, int c) { int b = 2; switch (a) @@ -22,6 +22,21 @@ int case 5: b += 1; break; + case 6: + if (c == 2) + { + [[fallthrough]]; + } + else + { + [[fallthrough]]; + } + case 7: + b += 3; + [[fallthrough]]; + default: + b += 8; + break; } return b; } Index: gcc/testsuite/gcc.dg/c2x-attr-fallthrough-2.c =================================================================== --- gcc/testsuite/gcc.dg/c2x-attr-fallthrough-2.c (revision 278510) +++ gcc/testsuite/gcc.dg/c2x-attr-fallthrough-2.c (working copy) @@ -15,7 +15,8 @@ int z = sizeof (int [[fallthrough]]); /* { dg-erro int f (int a) { - [[fallthrough]] int b = 2; /* { dg-warning "not followed by|ignored" } */ + [[fallthrough]] int b = 2; /* { dg-warning "not followed by" } */ + /* { dg-error "ignored" "ignored" { target *-*-* } .-1 } */ switch (a) { case 1: Index: gcc/testsuite/gcc.dg/c2x-attr-fallthrough-3.c =================================================================== --- gcc/testsuite/gcc.dg/c2x-attr-fallthrough-3.c (revision 278510) +++ gcc/testsuite/gcc.dg/c2x-attr-fallthrough-3.c (working copy) @@ -1,5 +1,5 @@ /* Test C2x attribute syntax. Invalid use of fallthrough attribute - outside switch or in bad context inside switch. */ + outside switch. */ /* { dg-do compile } */ /* { dg-options "-std=c2x -pedantic-errors -Wextra" } */ @@ -7,12 +7,5 @@ int f (int a) { [[fallthrough]]; /* { dg-error "invalid use of attribute 'fallthrough'" } */ - switch (a) - { - case 1: - a++; - [[fallthrough]]; /* { dg-warning "attribute 'fallthrough' not preceding a case label or default label" } */ - a++; - } return a; } Index: gcc/testsuite/gcc.dg/c2x-attr-fallthrough-6.c =================================================================== --- gcc/testsuite/gcc.dg/c2x-attr-fallthrough-6.c (nonexistent) +++ gcc/testsuite/gcc.dg/c2x-attr-fallthrough-6.c (working copy) @@ -0,0 +1,18 @@ +/* Test C2x attribute syntax. Invalid use of fallthrough attribute in + bad context inside switch. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors -Wextra" } */ + +int +f (int a) +{ + switch (a) + { + case 1: + a++; + [[fallthrough]]; /* { dg-error "attribute 'fallthrough' not preceding a case label or default label" } */ + a++; + [[fallthrough]]; /* { dg-error "attribute 'fallthrough' not preceding a case label or default label" } */ + } + return a; +}