clang generates warnings if use preprocessed files.

[llvmbot]

Bugzilla Link	30529
Resolution	WONTFIX
Resolved on	Sep 26, 2016 16:24
Version	unspecified
OS	Linux
Blocks	#24719
Reporter	LLVM Bugzilla Contributor
CC	@zygoloid

Extended Description

#define T(x) (x==1)

int main(){
int x = 1;
if (T(x)) {
return 0;}
return 1;
}

clang -Wall a.c returns no warning.

clang a.c -E > a.i

clang -Wall a.i

returns

a.c:5:9: warning: equality comparison with extraneous parentheses [-Wparentheses-equality]
if ((x==1)) {
~^~~
a.c:5:9: note: remove extraneous parentheses around the comparison to silence this warning
if ((x==1)) {
~ ^ ~
a.c:5:9: note: use '=' to turn this equality comparison into an assignment
if ((x==1)) {
^~
=
1 warning generated.

[zygoloid]

We do not consider this to be a bug. We have heuristics in our warnings that depend on whether the tokens come from a macro expansion, so it is expected that preprocessed source will sometimes produce different warnings.

If you want to avoid this, use -E -frewrite-includes instead of just -E.