FAIL ./check.t:arith-ternary-prec-1 with GCC >= 6.3 and LTO

[Jan Palus]

Not really sure where the issue is, whether it's mksh or gcc, but I'll try here first.

Since GCC 6.3 (also present in 6.4, didn't check 7.x) I get reproducible failure in tests if mksh was built with LTO:

sh ./Build.sh -c lto
...
./tests.sh
...
FAIL ./check.t:arith-ternary-prec-1
 Description:
  Check precedence of ternary operator vs assignment
 unexpected exit status 0 (exit-code 0), expected e != 0
 unexpected stderr - wanted pattern:
  /.*:.*1 \? 20 : x\+=2.*lvalue.*\n$/
 got nothing

If I run input from test:

        typeset -i x=2
        y=$((1 ? 20 : x+=2))

the value of y is 22.

[Thorsten Glaser (mirabilos)]

It’s known that mksh’s testsuite exhibits problems in the infrastructure (kernel, libraries, toolchain, compiler).

In this case, GCC’s LTO (and before that, -fwhole-program --combine) is a repeat offender of breaking code.

If your builds exhibit this problem, you should *disable LTO for your _entire_ operating system*. (I’ve seen this GCC version produce LTO bugs on other distros as well, it’s wrong code generation, but LTO bugs are not interesting to GCC developers.)