Can not use C99 function names as variable names in C89

Description

int logf = 5;
int main() {
        return logf;
}

# gcc test.c -o test -std=c89
# ./test; echo $?
5
# clang test.c -o test -std=c89
test.c:1:5: error: redefinition of 'logf' as different kind of symbol
int logf = 5;
    ^
test.c:1:5: note: previous definition is here
test.c:4:16: warning: incompatible pointer to integer conversion returning 'float (float)' from a function with result type 'int' [-Wint-conversion]
        return logf;
               ^~~~
1 warning and 1 error generated.

Contributor guide

Tech stack

ccpp

Domain

backend

Issue type

bug

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

4

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

3-5 days

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

C programmingC standards (C89, C99)Compiler architecture

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

15

Research direction

Check the clang source code for handling of C89 vs C99 built in functions. Look at the tokenizer and identifier resolution for math functions like logf. The issue suggests that clang incorrectly treats logf as a built in function in C89 mode, while gcc does not. A fix might involve adjusting the list of reserved identifiers per C standard or the name lookup logic in Sema or Parser. Review relevant code in include/clang/Basic/Builtins.def and lib/Sema/. Ensure that in C89 mode, C99 only built ins are not treated as reserved.