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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id e21-20020ac845d5000000b003431446588fsm6504515qto.5.2022.12.19.11.56.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Dec 2022 11:56:55 -0800 (PST) Message-ID: <4ce20330-1026-a444-661f-6571f16e05bf@redhat.com> Date: Mon, 19 Dec 2022 14:56:55 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH] c++: NTTP object wrapper substitution fixes [PR103346, ...] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org References: <20221206175702.987794-1-ppalka@redhat.com> <98f22062-9f4e-0406-cddc-cfd49a63c3e8@idea> <6596764b-d032-ef6e-1566-7c21668def8a@idea> From: Jason Merrill In-Reply-To: <6596764b-d032-ef6e-1566-7c21668def8a@idea> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-13.0 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 12/19/22 13:13, Patrick Palka wrote: > On Mon, 19 Dec 2022, Jason Merrill wrote: > >> On 12/6/22 13:35, Patrick Palka wrote: >>> This patch fixes some issues with substitution into a C++20 template >>> parameter object wrapper: >>> >>> * The first testcase demonstrates a situation where the same_type_p >>> assert in relevant case of tsubst_copy doesn't hold, because (partial) >>> substitution of {int,} into the VIEW_CONVERT_EXPR wrapper yields >>> A but substitution into the underlying TEMPLATE_PARM_INDEX is a >>> nop and yields A due to tsubst's level == 1 early exit test. >> >> We exit in that case because continuing would reduce the level to an >> impossible 0. Why doesn't the preceding code find a binding for T? > > Whoops, I misspoke. The problem is that there's no binding for V since > only T=int was explicitly specified, so when substituting into the > TEMPLATE_PARM_INDEX for V in 'void f(B)', we hit that early exit and > never get a chance to substitute T=int into the tpi's TREE_TYPE (which > would yield A as desired). So the TREE_TYPE of the wrapped tpi > remains A whereas the substituted TREE_TYPE of the wrapper is A, > a mismatch. Ah, makes sense. The patch is OK. >> >>> So >>> this patch just gets rid of the assert; the type mismatch doesn't >>> seem to be a problem in practice, I suppose because the coercion is >>> from one dependent type to another. >>> >>> * In the second testcase, dependent substitution into the underlying >>> TEMPLATE_PARM_INDEX yields a CALL_EXPR with empty TREE_TYPE, which >>> tsubst_copy doesn't expect. This patch fixes this by handling empty >>> TREE_TYPE the same way as a non-const TREE_TYPE. Moreover, after >>> this substitution we're left with a VIEW_CONVERT_EXPR wrapping a >>> CALL_EXPR instead of a TEMPLATE_PARM_INDEX, which during the subsequent >>> non-dependent substitution tsubst_copy doesn't expect either. So >>> this patch also relaxes tsubst_copy to accept such VIEW_CONVERT_EXPR >>> too. >>> >>> * In the third testcase, we end up never resolving the call to >>> f.modify() since tsubst_copy doesn't do overload resolution. >>> This patch fixes this by moving the handling of these >>> VIEW_CONVERT_EXPR wrappers from tsubst_copy to tsubst_copy_and_build. >>> For good measure tsubst_copy_and_build should also handle >>> REF_PARENTHESIZED_P wrappers instead of delegating to tsubst_copy. >>> >>> After this patch, VIEW_CONVERT_EXPR substitution is ultimately just >>> moved from tsubst_copy to tsubst_copy_and_build and made more >>> permissive. >>> >>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for >>> trunk? >>> >>> PR c++/103346 >>> PR c++/104278 >>> PR c++/102553 >>> >>> gcc/cp/ChangeLog: >>> >>> * pt.cc (tsubst_copy) : In the handling >>> of C++20 template parameter object wrappers: Remove same_type_p >>> assert. Accept non-TEMPLATE_PARM_INDEX inner operand. Handle >>> empty TREE_TYPE on substituted inner operand. Move it to ... >>> (tsubst_copy_and_build): ... here. Also handle REF_PARENTHESIZED_P >>> VIEW_CONVERT_EXPRs. >>> >>> gcc/testsuite/ChangeLog: >>> >>> * g++.dg/cpp2a/nontype-class52a.C: New test. >>> * g++.dg/cpp2a/nontype-class53.C: New test. >>> * g++.dg/cpp2a/nontype-class54.C: New test. >>> * g++.dg/cpp2a/nontype-class55.C: New test. >>> --- >>> gcc/cp/pt.cc | 73 ++++++++++--------- >>> gcc/testsuite/g++.dg/cpp2a/nontype-class52a.C | 15 ++++ >>> gcc/testsuite/g++.dg/cpp2a/nontype-class53.C | 25 +++++++ >>> gcc/testsuite/g++.dg/cpp2a/nontype-class54.C | 23 ++++++ >>> gcc/testsuite/g++.dg/cpp2a/nontype-class55.C | 15 ++++ >>> 5 files changed, 116 insertions(+), 35 deletions(-) >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class52a.C >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class53.C >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class54.C >>> create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class55.C >>> >>> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc >>> index 2d8e4fdd4b5..0a196f069ad 100644 >>> --- a/gcc/cp/pt.cc >>> +++ b/gcc/cp/pt.cc >>> @@ -17271,42 +17271,16 @@ tsubst_copy (tree t, tree args, tsubst_flags_t >>> complain, tree in_decl) >>> return maybe_wrap_with_location (op0, EXPR_LOCATION (t)); >>> } >>> tree op = TREE_OPERAND (t, 0); >>> - if (code == VIEW_CONVERT_EXPR >>> - && TREE_CODE (op) == TEMPLATE_PARM_INDEX) >>> - { >>> - /* Wrapper to make a C++20 template parameter object const. */ >>> - op = tsubst_copy (op, args, complain, in_decl); >>> - if (!CP_TYPE_CONST_P (TREE_TYPE (op))) >>> - { >>> - /* The template argument is not const, presumably because >>> - it is still dependent, and so not the const template parm >>> - object. */ >>> - tree type = tsubst (TREE_TYPE (t), args, complain, in_decl); >>> - gcc_checking_assert >>> (same_type_ignoring_top_level_qualifiers_p >>> - (type, TREE_TYPE (op))); >>> - if (TREE_CODE (op) == CONSTRUCTOR >>> - || TREE_CODE (op) == IMPLICIT_CONV_EXPR) >>> - { >>> - /* Don't add a wrapper to these. */ >>> - op = copy_node (op); >>> - TREE_TYPE (op) = type; >>> - } >>> - else >>> - /* Do add a wrapper otherwise (in particular, if op is >>> - another TEMPLATE_PARM_INDEX). */ >>> - op = build1 (code, type, op); >>> - } >>> - return op; >>> - } >>> /* force_paren_expr can also create a VIEW_CONVERT_EXPR. */ >>> - else if (code == VIEW_CONVERT_EXPR && REF_PARENTHESIZED_P (t)) >>> + if (code == VIEW_CONVERT_EXPR && REF_PARENTHESIZED_P (t)) >>> { >>> op = tsubst_copy (op, args, complain, in_decl); >>> op = build1 (code, TREE_TYPE (op), op); >>> REF_PARENTHESIZED_P (op) = true; >>> return op; >>> } >>> - /* We shouldn't see any other uses of these in templates. */ >>> + /* We shouldn't see any other uses of these in templates >>> + (tsubst_copy_and_build handles C++20 tparm object wrappers). */ >>> gcc_unreachable (); >>> } >>> @@ -21569,12 +21543,41 @@ tsubst_copy_and_build (tree t, >>> case NON_LVALUE_EXPR: >>> case VIEW_CONVERT_EXPR: >>> - if (location_wrapper_p (t)) >>> - /* We need to do this here as well as in tsubst_copy so we get the >>> - other tsubst_copy_and_build semantics for a PARM_DECL operand. */ >>> - RETURN (maybe_wrap_with_location (RECUR (TREE_OPERAND (t, 0)), >>> - EXPR_LOCATION (t))); >>> - /* fallthrough. */ >>> + { >>> + tree op = RECUR (TREE_OPERAND (t, 0)); >>> + if (location_wrapper_p (t)) >>> + /* We need to do this here as well as in tsubst_copy so we get the >>> + other tsubst_copy_and_build semantics for a PARM_DECL operand. >>> */ >>> + RETURN (maybe_wrap_with_location (op, EXPR_LOCATION (t))); >>> + >>> + gcc_checking_assert (TREE_CODE (t) == VIEW_CONVERT_EXPR); >>> + if (REF_PARENTHESIZED_P (t)) >>> + /* force_paren_expr can also create a VIEW_CONVERT_EXPR. */ >>> + RETURN (finish_parenthesized_expr (op)); >>> + >>> + /* Otherwise, we're dealing with a wrapper to make a C++20 template >>> + parameter object const. */ >>> + if (TREE_TYPE (op) == NULL_TREE >>> + || !CP_TYPE_CONST_P (TREE_TYPE (op))) >>> + { >>> + /* The template argument is not const, presumably because >>> + it is still dependent, and so not the const template parm >>> + object. */ >>> + tree type = tsubst (TREE_TYPE (t), args, complain, in_decl); >>> + if (TREE_CODE (op) == CONSTRUCTOR >>> + || TREE_CODE (op) == IMPLICIT_CONV_EXPR) >>> + { >>> + /* Don't add a wrapper to these. */ >>> + op = copy_node (op); >>> + TREE_TYPE (op) = type; >>> + } >>> + else >>> + /* Do add a wrapper otherwise (in particular, if op is >>> + another TEMPLATE_PARM_INDEX). */ >>> + op = build1 (VIEW_CONVERT_EXPR, type, op); >>> + } >>> + RETURN (op); >>> + } >>> default: >>> /* Handle Objective-C++ constructs, if appropriate. */ >>> diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class52a.C >>> b/gcc/testsuite/g++.dg/cpp2a/nontype-class52a.C >>> new file mode 100644 >>> index 00000000000..ae5d5df70ac >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class52a.C >>> @@ -0,0 +1,15 @@ >>> +// A version of nontype-class52.C where explicit template arguments are >>> +// given in the call to f (which during deduction need to be partially >>> +// substituted into the NTTP object V in f's signature). >>> +// { dg-do compile { target c++20 } } >>> + >>> +template struct A { }; >>> + >>> +template struct B { }; >>> + >>> +template V> void f(B); >>> + >>> +int main() { >>> + constexpr A a; >>> + f(B{}); >>> +} >>> diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class53.C >>> b/gcc/testsuite/g++.dg/cpp2a/nontype-class53.C >>> new file mode 100644 >>> index 00000000000..9a6398c5f57 >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class53.C >>> @@ -0,0 +1,25 @@ >>> +// PR c++/103346 >>> +// { dg-do compile { target c++20 } } >>> + >>> +struct Item {}; >>> + >>> +template >>> +struct Sequence { }; >>> + >>> +template >>> +using ItemSequence = Sequence; >>> + >>> +template >>> +constexpr auto f() { >>> + constexpr auto l = [](Item item) { return item; }; >>> + return ItemSequence{}; >>> +} >>> + >>> +using ty0 = decltype(f<>()); >>> +using ty0 = ItemSequence<>; >>> + >>> +using ty1 = decltype(f<{}>()); >>> +using ty1 = ItemSequence<{}>; >>> + >>> +using ty3 = decltype(f<{}, {}, {}>()); >>> +using ty3 = ItemSequence<{}, {}, {}>; >>> diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class54.C >>> b/gcc/testsuite/g++.dg/cpp2a/nontype-class54.C >>> new file mode 100644 >>> index 00000000000..8127b1f5426 >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class54.C >>> @@ -0,0 +1,23 @@ >>> +// PR c++/104278 >>> +// { dg-do compile { target c++20 } } >>> + >>> +struct foo { >>> + int value; >>> + constexpr foo modify() const { return { value + 1 }; } >>> +}; >>> + >>> +template >>> +struct bar { >>> + static void run() { } >>> +}; >>> + >>> +template >>> +struct qux { >>> + static void run() { >>> + bar::run(); >>> + } >>> +}; >>> + >>> +int main() { >>> + qux::run(); >>> +} >>> diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class55.C >>> b/gcc/testsuite/g++.dg/cpp2a/nontype-class55.C >>> new file mode 100644 >>> index 00000000000..afcb3d64495 >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class55.C >>> @@ -0,0 +1,15 @@ >>> +// PR c++/102553 >>> +// { dg-do compile { target c++20 } } >>> + >>> +struct s1{}; >>> +template inline constexpr s1 ch{}; >>> + >>> +template struct s2{}; >>> +template using alias1 = s2; >>> + >>> +template >>> +void general(int n) { >>> + alias1>{}; >>> +} >>> + >>> +template void general(int); >> >> >