[PATCH] D140210: [IPSCCP] Enable specialization of functions.

Tue Jan 10 07:13:56 PST 2023

labrinea added a comment.
Herald added a subscriber: StephenFan.

After some experimentation I found that the specialization of `spec_qsort` with `case_bit_test_cmp` as the compare function causes the problem. Digging a little more in the SPEC documentation I found these portability issues which seem to manifest when FuncSpec is enabled:

- https://www.spec.org/cpu2017/Docs/benchmarks/502.gcc_r.html#Portability

> spec_qsort and ANSI aliasing: The spec_qsort.c routine does not strictly obey the ANSI aliasing rules. See the detailed discussion in the documentation for 505.mcf_r, which is where the problem was reported.

- https://www.spec.org/cpu2017/Docs/benchmarks/505.mcf_r.html#Portability

> Some users of GCC 6 (and later) have reported that 505.mcf_r gets wrong answers when compiled with both link-time optimization (LTO) and feedback-directed optimization (FDO), for example at GCC bugzilla 83201.

After I applied the patch attached on that ticket (https://gcc.gnu.org/bugzilla/attachment.cgi?id=42919&action=diff) to the SPEC sources the failure went away. I am puzzled because when cloning a function we do preserve the TBAA medatate if any.

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https://reviews.llvm.org/D140210