Re: [PATCH] c++: Avoid strict_aliasing_warning on dependent types or expressions [PR94951]
On 5/5/20 6:28 PM, Jakub Jelinek wrote: Hi! The following testcase gets a bogus warning during build_base_path, when cp_build_indirect_ref* calls strict_aliasing_warning with a dependent expression. IMHO calling get_alias_set etc. on dependent types feels wrong to me, we should just defer the warnings in those cases until instantiation and only handle the cases where neither type nor expr are dependent. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? OK. 2020-05-05 Jakub Jelinek PR c++/94951 * typeck.c (cp_strict_aliasing_warning): New function. (cp_build_indirect_ref_1, build_reinterpret_cast_1): Use it instead of strict_aliasing_warning. * g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C: New test. --- gcc/cp/typeck.c.jj 2020-03-19 22:54:38.393744684 +0100 +++ gcc/cp/typeck.c 2020-05-05 18:12:21.964090624 +0200 @@ -3318,6 +3318,22 @@ build_x_indirect_ref (location_t loc, tr return rval; } +/* Like c-family strict_aliasing_warning, but don't warn for dependent + types or expressions. */ + +static bool +cp_strict_aliasing_warning (location_t loc, tree type, tree expr) +{ + if (processing_template_decl) +{ + tree e = expr; + STRIP_NOPS (e); + if (dependent_type_p (type) || type_dependent_expression_p (e)) + return false; +} + return strict_aliasing_warning (loc, type, expr); +} + /* The implementation of the above, and of indirection implied by other constructs. If DO_FOLD is true, fold away INDIRECT_REF of ADDR_EXPR. */ @@ -3360,10 +3376,10 @@ cp_build_indirect_ref_1 (location_t loc, /* If a warning is issued, mark it to avoid duplicates from the backend. This only needs to be done at warn_strict_aliasing > 2. */ - if (warn_strict_aliasing > 2) - if (strict_aliasing_warning (EXPR_LOCATION (ptr), -type, TREE_OPERAND (ptr, 0))) - TREE_NO_WARNING (ptr) = 1; + if (warn_strict_aliasing > 2 + && cp_strict_aliasing_warning (EXPR_LOCATION (ptr), +type, TREE_OPERAND (ptr, 0))) + TREE_NO_WARNING (ptr) = 1; } if (VOID_TYPE_P (t)) @@ -,7 +7793,7 @@ build_reinterpret_cast_1 (location_t loc expr = cp_build_addr_expr (expr, complain); if (warn_strict_aliasing > 2) - strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); + cp_strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); if (expr != error_mark_node) expr = build_reinterpret_cast_1 @@ -7891,7 +7907,7 @@ build_reinterpret_cast_1 (location_t loc if (warn_strict_aliasing <= 2) /* strict_aliasing_warning STRIP_NOPs its expr. */ - strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); + cp_strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); return build_nop_reinterpret (type, expr); } --- gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C.jj 2020-05-05 18:18:43.40832 +0200 +++ gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C 2020-05-05 18:17:35.178352212 +0200 @@ -0,0 +1,12 @@ +// PR c++/94951 +// { dg-do compile } +// { dg-options "-O2 -Wall" } + +struct A { int a; }; +template +struct B : public A +{ + static B foo () { B t; t.a = 4; return t; }// { dg-bogus "dereferencing type-punned pointer will break strict-aliasing rules" } +}; + +B<0> b = B<0>::foo (); Jakub
[PATCH] c++: Avoid strict_aliasing_warning on dependent types or expressions [PR94951]
Hi! The following testcase gets a bogus warning during build_base_path, when cp_build_indirect_ref* calls strict_aliasing_warning with a dependent expression. IMHO calling get_alias_set etc. on dependent types feels wrong to me, we should just defer the warnings in those cases until instantiation and only handle the cases where neither type nor expr are dependent. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2020-05-05 Jakub Jelinek PR c++/94951 * typeck.c (cp_strict_aliasing_warning): New function. (cp_build_indirect_ref_1, build_reinterpret_cast_1): Use it instead of strict_aliasing_warning. * g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C: New test. --- gcc/cp/typeck.c.jj 2020-03-19 22:54:38.393744684 +0100 +++ gcc/cp/typeck.c 2020-05-05 18:12:21.964090624 +0200 @@ -3318,6 +3318,22 @@ build_x_indirect_ref (location_t loc, tr return rval; } +/* Like c-family strict_aliasing_warning, but don't warn for dependent + types or expressions. */ + +static bool +cp_strict_aliasing_warning (location_t loc, tree type, tree expr) +{ + if (processing_template_decl) +{ + tree e = expr; + STRIP_NOPS (e); + if (dependent_type_p (type) || type_dependent_expression_p (e)) + return false; +} + return strict_aliasing_warning (loc, type, expr); +} + /* The implementation of the above, and of indirection implied by other constructs. If DO_FOLD is true, fold away INDIRECT_REF of ADDR_EXPR. */ @@ -3360,10 +3376,10 @@ cp_build_indirect_ref_1 (location_t loc, /* If a warning is issued, mark it to avoid duplicates from the backend. This only needs to be done at warn_strict_aliasing > 2. */ - if (warn_strict_aliasing > 2) - if (strict_aliasing_warning (EXPR_LOCATION (ptr), -type, TREE_OPERAND (ptr, 0))) - TREE_NO_WARNING (ptr) = 1; + if (warn_strict_aliasing > 2 + && cp_strict_aliasing_warning (EXPR_LOCATION (ptr), +type, TREE_OPERAND (ptr, 0))) + TREE_NO_WARNING (ptr) = 1; } if (VOID_TYPE_P (t)) @@ -,7 +7793,7 @@ build_reinterpret_cast_1 (location_t loc expr = cp_build_addr_expr (expr, complain); if (warn_strict_aliasing > 2) - strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); + cp_strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); if (expr != error_mark_node) expr = build_reinterpret_cast_1 @@ -7891,7 +7907,7 @@ build_reinterpret_cast_1 (location_t loc if (warn_strict_aliasing <= 2) /* strict_aliasing_warning STRIP_NOPs its expr. */ - strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); + cp_strict_aliasing_warning (EXPR_LOCATION (expr), type, expr); return build_nop_reinterpret (type, expr); } --- gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C.jj 2020-05-05 18:18:43.40832 +0200 +++ gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C 2020-05-05 18:17:35.178352212 +0200 @@ -0,0 +1,12 @@ +// PR c++/94951 +// { dg-do compile } +// { dg-options "-O2 -Wall" } + +struct A { int a; }; +template +struct B : public A +{ + static B foo () { B t; t.a = 4; return t; }// { dg-bogus "dereferencing type-punned pointer will break strict-aliasing rules" } +}; + +B<0> b = B<0>::foo (); Jakub