RFR: 8255416: Investigate err_msg to detect unnecessary uses

[Thomas Stuefe]

On Wed, 28 Oct 2020 16:46:47 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

> Hi,
> 
> When a single string without formatting arguments is provided to `err_msg`, it's redundancy, as the same message could be used without any err_msg. This is a follow-up to the discussion https://github.com/openjdk/jdk/pull/812#discussion_r511784050
> 
> Please review a change that makes `err_msg` with a single string to fail compilation. 
> 
> Detected uses of err_msg with a single string were eliminated as well.

Changes requested by stuefe (Reviewer).

src/hotspot/share/gc/shenandoah/mode/shenandoahMode.hpp line 44:

> 42:     if ((name)) {                                                           \
> 43:       const char* msg = "GC mode needs -XX:-" #name " to work correctly";   \
> 44:       vm_exit_during_initialization("Error", msg);                          \

Same as above, can be inlined into one call. No need for the temporary variable.

src/hotspot/share/utilities/formatBuffer.hpp line 124:

> 122:   // If compilation fails because of ambiguity between this and real constructor, you
> 123:   // could drop err_msg use at all.
> 124:   inline FormatErrBuffer(const char* msg) { ShouldNotReachHere(); }

I do not think this is a good idea (apart from it being too complex for a not that serious issue).

The asserts fire, of course, only at runtime. But this function is used usually in some error context, as part of of error reporting. I do not think our tests cover all those paths.

Either somehow make this a compile time error or just leave it as it is. We also could, since this buffer object is used usually as input for vm_exit_during_initialization(), give that function a var-arg overload.

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PR: https://git.openjdk.java.net/jdk/pull/905