https://llvm.org/bugs/show_bug.cgi?id=28918
Bug ID: 28918
Summary: -Wunreachable-code warning involving templated local
variable can't be suppressed with extra parentheses
Product: clang
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Frontend
Assignee: unassignedclangb...@nondot.org
Reporter: cpeter...@mozilla.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 16922
--> https://llvm.org/bugs/attachment.cgi?id=16922&action=edit
test.cpp
-Wunreachable-code warning involving templated local variable can't be
suppressed with extra parentheses. I suppressed a -Wunreachable-code warning in
Firefox earlier this year [1] by adding extra parentheses, as suggested by
Xcode's clang on OS X. Unfortunately, this Firefox warning is back [2] because
clang 3.9 on Linux no longer recognizes the parentheses suppression.
Attached is a standalone test case that reproduces the insuppressible warning
even with Xcode's clang (Apple LLVM version 7.3.0 (clang-703.0.31)). So there
is a latent clang bug plus a regression that caused Firefox's
previously-suppressible warning to no longer be suppressible.
The warning looks like it might only happen when the boolean condition involves
an expression with a templated type. In the test case below, a templated local
variable gets copy-constructed to form an argument to a boolean
helper-function.
$ clang++ -Wunreachable-code test.cpp
test.cpp:23:5: warning: code will never be executed [-Wunreachable-code]
printf("Does clang warn about this code being unreachable?\n");
^~~~~~
1 warning generated.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1223265
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1291397
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