[PATCH] D59201: [RegAllocHints] Avoid compile time regression

[Dimitry Andric via Phabricator via llvm-commits]

dim added a comment.

This helps quite a lot, in the sense that my original test case from PR40986 now at least compiles within a finite time.  There is still a performance loss between clang 7.0.1 and clang 8.0.0 with this patch, though (tested with 10 runs each):

  x clang-7.0.1-realtime.txt
  + clang-8.0.0-realtime.txt
  +--------------------------------------------------------------------------------------------------+
  |    x     x                                                         +                             |
  |x   x  x  x    xx          x                  x  +         +++++    ++                           +|
  ||_________M___A_____________|                        |_________M__A___________|                   |
  +--------------------------------------------------------------------------------------------------+
      N           Min           Max        Median           Avg        Stddev
  x  10         37.19          40.4         37.89         38.16    0.94949109
  +  10         40.56         43.91        41.525        41.732    0.86639483
  Difference at 95.0% confidence
          3.572 +/- 0.853992
          9.36059% +/- 2.35454%
          (Student's t, pooled s = 0.908893)

So roughly 9% slower in real time (user time measurements give almost the same result, since this is all single-threaded of course.)


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https://reviews.llvm.org/D59201