RFR: 8257928: Test image build failure with clang-10 due to -Wmisleading-indentation

[Chris Plummer]

On Wed, 9 Dec 2020 07:11:53 GMT, Hao Sun <github.com+16932759+shqking at openjdk.org> wrote:

> Flag '-Wmisleading-indentation' was introduced since clang-10 [1] and
> gcc-6 [2]. Putting the code with proper indentations would suppress this
> warning.
> 
> The main reason why test image build with gcc succeeds is that, clang
> and gcc might behave differently for some corner cases under
> '-Wmisleading-indentation'.
> 
> The following code snippet is crafted based on this build failure, where
> each statement with improper indentation (line A and line B) follows an
> if-statement. The key difference between foo() and bar() lies in that
> there exists an extra comment, i.e. "/* comment 2 */", between statement
> at line A and the if-statement.
> 
>     int foo(int num) {
>       /* comment 1 */
>       if (num > 1)
>         return 0;
> 
>       /* comment 2 */
>         num = num + 1;  // line A
>       return num;
>     }
> 
>     int bar(int val) {
>       /* comment 3 */
>       if (val > 1)
>         return 0;
> 
>         val = val + 1;  // line B
>       return val;
>     }
> 
> It's worth noting that foo() is quite similar to the erroneous code in
> this build failure. Clang-10 would emit misleading indentation warnings
> for both foo() and bar(), whereas gcc-6 or higher considers foo() free
> of problems. [3]
> 
> This patch is a complement to JDK-8253892. In JDK-8253892, flag
> '-Wmisleading-indentation' is disabled for both clang and gcc when
> building JRE and JDK images. This patch does not disable the flag for
> test image building, but just fixes the code, becasue:
>   - only a small number of warnings are produced and it's easy to fix
>   them one by one.
>   - inconsistent warning behaviors between gcc and clang are triggered
>   by this case and simply disabling the flag does not work.
> 
> Note that AArch64 is NOT tested because test image build still fails
> after this bug is fixed due to another runtime error (See JDK-8257936),
> which is not related to this patch.
> 
> [1] https://releases.llvm.org/10.0.0/tools/clang/docs/DiagnosticsReference.html
> [2] https://gcc.gnu.org/onlinedocs/gcc-6.5.0/gcc/Warning-Options.html#Warning-Options
> [3] https://godbolt.org/z/xs6xWv
> 
> ---------------------
> We have tested with this patch, the test image can be built successfully with clang-10 on Linux X86 machine.

Marked as reviewed by cjplummer (Reviewer).

-------------

PR: https://git.openjdk.java.net/jdk/pull/1709