[ARM] Don't use the Machine Scheduler for cortex-m at minsize

The new cortex-m schedule in rL360768 helps performance, but can increase the
amount of high-registers used. This, on average, ends up increasing the
codesize by a fair amount (because less instructions are converted from T2 to
T1). On cortex-m at -Oz, where we are quite size-paranoid, it is better to use
the existing DAG scheduler with the RegPressure scheduling preference (at least
until the issues around T2 vs T1 instructions can be improved).

I have also made sure that the Sched::RegPressure dag scheduler is always
chosen for MinSize.

The test shows one case where we increase the number of registers used.

Differential Revision: https://reviews.llvm.org/D61882

llvm-svn: 360769
3 files changed
tree: 30c258c265b875e2dbc84bc9b56113156f6326b1
  1. .arcconfig
  2. .clang-format
  3. .clang-tidy
  4. .gitignore
  5. README.md
  6. clang-tools-extra/
  7. clang/
  8. compiler-rt/
  9. debuginfo-tests/
  10. libclc/
  11. libcxx/
  12. libcxxabi/
  13. libunwind/
  14. lld/
  15. lldb/
  16. llgo/
  17. llvm/
  18. openmp/
  19. parallel-libs/
  20. polly/
  21. pstl/

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