https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96749
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Iain D Sandoe <ia...@gcc.gnu.org>: https://gcc.gnu.org/g:8fba8178ac49493ed7998fb9008810aac8138c19 commit r10-9515-g8fba8178ac49493ed7998fb9008810aac8138c19 Author: Iain Sandoe <i...@sandoe.co.uk> Date: Tue Mar 2 10:12:58 2021 +0000 coroutines : Avoid generating empty statements [PR96749]. In the compiler-only idiom: " a = (target expr creats temp, op uses temp) " the target expression variable needs to be promoted to a frame one (if the expression has a suspend point). However, the only uses of the var are in the second part of the compound expression - and we were creating an empty statement corresponding to the (now unused) first arm. This then produces the spurious warnings noted. Fixed by avoiding generation of a separate variable nest for isolated target expressions (or similarly isolated co_awaits used in a function call). gcc/cp/ChangeLog: PR c++/96749 * coroutines.cc (flatten_await_stmt): Allow for the case where a target expression variable only has uses in the second part of a compound expression. (maybe_promote_temps): Avoid emiting empty statements. gcc/testsuite/ChangeLog: PR c++/96749 * g++.dg/coroutines/pr96749-1.C: New test. * g++.dg/coroutines/pr96749-2.C: New test. (cherry picked from commit ed8198461735f9b5b3c2cbe50f9913690ce4b4ca)
