https://bugs.llvm.org/show_bug.cgi?id=41420
Bug ID: 41420
Summary: missed opt: nounwind on extern "C"
Product: clang
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: LLVM Codegen
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected]
Clang fails to mark `extern "C"` functions as `nounwind`
(https://gcc.godbolt.org/z/GpX96P):
extern "C" int foo(int);
int bar(int x) { return foo(x); }
when compiled with clang -O3 -g0 -S emit-llvm produces:
define dso_local i32 @_Z3bari(i32) local_unnamed_addr #0 {
%2 = tail call i32 @foo(i32 %0)
ret i32 %2
}
declare dso_local i32 @foo(i32) local_unnamed_addr #1
attributes #0 = { uwtable "correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false" "less-precise-fpmad"="false"
"min-legal-vector-width"="0" "no-frame-pointer-elim"="false"
"no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false" "no-trapping-math"="false"
"stack-protector-buffer-size"="8" "target-cpu"="x86-64"
"target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false"
"use-soft-float"="false" }
attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false" "less-precise-fpmad"="false"
"no-frame-pointer-elim"="false" "no-infs-fp-math"="false"
"no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
"no-trapping-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
"unsafe-fp-math"="false" "use-soft-float"="false" }
where `foo` does not have the `nounwind` attribute.
The dcl.link section of the standard (http://eel.is/c++draft/dcl.link) makes
it, however, clear, that `extern "C"` is for linking against the C programming
language, which is an ABI that cannot throw any exceptions.
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