> > I believe this would be logically wrong, as the other versions still
> > wouldn't compile if you changed the relevant debug Pcds. (Which are
> > logically independent of the compile and link options - e.g. what if for
> > some reason you wanted to single step with the Debug Pcds set to
> > disabled, in a NOOPT build?)
>
> I don't think that use case exists in practice.
>
> Anyway, my suggestion is based on prior art: I *think* we ask gcc to
> whine about unused local variables in RELEASE builds only, too. See
> commits 20d00edf21d2 ("BaseTools/GCC: set -Wno-unused-but-set-variables
> only on RELEASE builds", 2016-03-25) and 8b6366f87584 ("BaseTools/GCC:
> set -Wno-unused-const-variable on RELEASE builds", 2017-09-08).
>
> ... TBH I don't understand the current state of
> "-Wno-unused-but-set-variables" and "-Wno-unused-const-variable" between
> X64 and AARCH64, considering the DEBUG target. Today,
> DEBUG_GCC5_AARCH64_CC_FLAGS disables these warnings, but
> DEBUG_GCC5_X64_CC_FLAGS doesn't, even though *both* macros specify
> -flto. Compare commit 06c8a34cc4bc ("BaseTool/tools_def GCC5: enable
> optimization for ARM/AARCH64 DEBUG builds", 2017-12-08) -- I don't
> understand why "-flto" had to be accompanied by
> "-Wno-unused-but-set-variable -Wno-unused-const-variable" in that commit.
>
> In brief, IA32 and X64 prior art supports my suggestion to shut up the
> warning only for RELEASE (for CLANGPDB too), but ARM/AARCH64 prior art
> contradicts that proposal. IOW, prior art is inconsistent per se... I
> don't understand.
>
> Laszlo
Hunting around further, it is not the Pcds which are causing this to
be optimised away, but the definition of MDEPKG_NDEBUG.
A completely different approach, which allows clang to spot that the
usage has been 'optimised away' and so to not complain (and therefore
allows us to re-enable the warning in CLANGDWARF as well), is the
following:
--- a/MdePkg/Include/Library/DebugLib.h
+++ b/MdePkg/Include/Library/DebugLib.h
@@ -426,7 +426,10 @@ UnitTestDebugAssert (
} \
} while (FALSE)
#else
-#define DEBUG(Expression)
+#define DEBUG(Expression) \
+ if (FALSE) { \
+ _DEBUG (Expression); \
+ }
#endif
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