A.
Empty function bodies causes two problems for Darwin's linker (i) zero-length
FDEs and (ii) coincident label addresses that might point to items of
differing weakness.
B.
Trailing local labels can be problematic when they end a function because
similarly they might apparently point to a following weak function, leading
to the linker concluding that there's a pointer-diff to a weak symbol
(which is not allowed).
Both conditions arise from __builtin_unreachable() lowering to a barrier.
The solution for both is to emit some finite amount of code; in the case of A
a trap is emitted, in the case of B a nop.
gcc/
2016-11-27 Iain Sandoe <iain@codesourcery.com>
PR target/57438
* config/i386/i386.c (ix86_code_end): Note that we emitted code
where the function might otherwise appear empty for picbase thunks.
(ix86_output_function_epilogue): If we find a zero-sized function
assume that reaching it is UB and trap. If we find a trailing label
append a nop.
* config/rs6000/rs6000.c (rs6000_output_function_epilogue): If we
find a zero-sized function assume that reaching it is UB and trap.
If we find a trailing label, append a nop.
gcc/testsuite/
2016-11-27 Iain Sandoe <iain@codesourcery.com>
PR target/57438
* gcc.dg/pr57438-1.c: New Test.
* gcc.dg/pr57438-2.c: New Test.
From-SVN: r242897
