From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 367463858402; Fri, 24 Sep 2021 21:03:03 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 367463858402 From: "richard-gccbugzilla at metafoo dot co.uk" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/91292] Mangler incorrectly handles negative numbers in expressions Date: Fri, 24 Sep 2021 21:03:03 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Version: 9.1.0 X-Bugzilla-Keywords: ABI, wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: richard-gccbugzilla at metafoo dot co.uk X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 24 Sep 2021 21:03:03 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D91292 --- Comment #7 from Richard Smith --- (In reply to Patrick Palka from comment #3) > Hmm, but according to > http://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling.literal the > mangling of a negative integer literal is prefixed with "n", There is no such thing as a negative integer literal. The ABI document says "negative integer *values* are preceded with "n""; th= is case is reached when mangling fully-resolved template arguments via the ::=3D production, not when mangling an instantiation-dependent expression. For example, given template struct X {}; template void f(X, X<-1>) {} template void f<1>(X<-1>, X<-1>); the proper mangling is _Z1fILi1EEv1XIXmlT_ngLi1EEES0_ILin1EE using ngLi1E for the instantiation-dependent expression -1 and Lin1E for the non-instantiation-dependent value -1. (In reply to Patrick Palka from comment #4) > And if -(1) is to be mangled the same as -1, then shouldn't >=20 > template > typename std::enable_if<(int)sizeof(T) >=3D -(1), int>::type size1(T *t= ); >=20 > template > typename std::enable_if<(int)sizeof(T) >=3D -1, int>::type size1(T *t); >=20 > be considered two declarations of the same function? But IIUC that would > contradict [temp.over.link]p5, which says >=20 > Two expressions involving template parameters are considered equivalent= if > two function definitions containing the expressions would satisfy the > one-definition rule >=20 > but IIUC the one-definition rule fails here because -1 is not the same > (token-wise) as -(1). These declarations are functionally-equivalent but not equivalent, so a pro= gram is not permitted to contain both. That language rule exists in order to all= ow implementations to do things like ignore parentheses in mangling, as the Itanium C++ ABI does. Note that parentheses are never mangled (except for a weird corner case involving pointers to members), so if your argument were correct it would a= pply very broadly. For example, that argument would imply that -1 and (-1) would need different manglings.=