Bug 19320 – -cov and -O yield variable used before set

When building the unittest with this command: make -f posix.mak std/array.test I encountered the following error: std/array.d(4179): Error: variable theArray used before set When building the unittest for the entire hierarchy with this command: make -f posix.mak -j8 unittest I did not encounter the error and all the tests passed.

Attempting to provide more context to this Running `make -f posix.mak std/array.test` will run ``` ../dmd/generated/linux/release/64/dmd -od$T -conf= -I../druntime/import -w -de -dip25 -m64 -fPIC -transition=complex -O -release -dip1000 -main -unittest generated/linux/release/64/libphobos2.a -defaultlib= -debuglib= -L-ldl -cov -run std/array.d ``` Where $T should expand to a path similar to `/tmp/.dmd-run-test.XXXXXX` If you remove the `-cov` flag, the tests will build without any problem. This issue is related with the Code coverage instrumentation

Reduced with $ dustmite --no-redirect . "~/dlang/bin/dmddev -O -cov -unittest -main array.d 2>&1 | grep 'variable theArray used before set'" Resulting in: $ dmd -O -cov array.d ``` auto staticArray(U, T)(T) { U[] theArray = void; return theArray; } void main() { staticArray!(int, int)(3); } ``` Making it clear that this bug is a result of -O and -cov.

By adding a asm block with a `nop` instruction to the affected scope, the compiler optimizer will give up searching: asm { nop; }

@ljmf00 created dlang/phobos pull request #8204 "std.array: workaround for Issue 19320" mentioning this issue: - std.array: workaround for Issue 19320 By adding a asm block with a `nop` instruction to the affected scope, the compiler optimizer will give up searching. https://github.com/dlang/phobos/pull/8204

@RazvanN7 created dlang/dmd pull request #13015 "Fix Issue 19320 - -cov and -O yield variable used before set" fixing this issue: - Fix Issue 19320 - -cov and -O yield variable used before set https://github.com/dlang/dmd/pull/13015

Simplified: int[] staticArray(int) { int[] theArray = void; return theArray; } void main() { staticArray(3); }

dlang/dmd pull request #13015 "Fix Issue 19320 - -cov and -O yield variable used before set" was merged into master: - df0c19ec799a77b6b59bebd92ec0ed6c48870dd0 by RazvanN7: Fix Issue 19320 - -cov and -O yield variable used before set https://github.com/dlang/dmd/pull/13015