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Sanjay Patel 161c7d06da [EarlyCSE] avoid crashing when detecting min/max/abs patterns (PR41083)
As discussed in PR41083:
https://bugs.llvm.org/show_bug.cgi?id=41083
...we can assert/crash in EarlyCSE using the current hashing scheme and
instructions with flags.

ValueTracking's matchSelectPattern() may rely on overflow (nsw, etc) or
other flags when detecting patterns such as min/max/abs composed of
compare+select. But the value numbering / hashing mechanism used by
EarlyCSE intersects those flags to allow more CSE.

Several alternatives to solve this are discussed in the bug report.
This patch avoids the issue by doing simple matching of min/max/abs
patterns that never requires instruction flags. We give up some CSE
power because of that, but that is not expected to result in much
actual performance difference because InstCombine will canonicalize
these patterns when possible. It even has this comment for abs/nabs:

  /// Canonicalize all these variants to 1 pattern.
  /// This makes CSE more likely.

(And this patch adds PhaseOrdering tests to verify that the expected
transforms are still happening in the standard optimization pipelines.

I left this code to use ValueTracking's "flavor" enum values, so we
don't have to change the callers' code. If we decide to go back to
using the ValueTracking call (by changing the hashing algorithm
instead), it should be obvious how to replace this chunk.

Differential Revision: https://reviews.llvm.org/D74285
2020-02-10 17:25:34 -05:00
benchmarks
bindings Pass length of string in Go binding of CreateCompileUnit 2020-01-17 13:35:30 -08:00
cmake [CMake] Use LLVM tools external project build where possible 2020-02-07 13:43:30 -08:00
docs git bisect docs: formatting tweaks 2020-02-10 15:47:59 -05:00
examples [CMake] Add missing component dependencies, to fix building for mingw with BUILD_SHARED_LIBS 2020-02-05 13:10:27 +02:00
include [CallPromotionUtils] Add tryPromoteCall. 2020-02-10 13:43:16 -08:00
lib [EarlyCSE] avoid crashing when detecting min/max/abs patterns (PR41083) 2020-02-10 17:25:34 -05:00
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runtimes Revert "[CMake] Filter libc++abi and libunwind from runtimes build in MSVC" 2020-02-07 11:28:21 -08:00
test [EarlyCSE] avoid crashing when detecting min/max/abs patterns (PR41083) 2020-02-10 17:25:34 -05:00
tools Continue removing llgo. 2020-02-10 10:33:58 -08:00
unittests [CallPromotionUtils] Add tryPromoteCall. 2020-02-10 13:43:16 -08:00
utils [gn build] Port bb383ae6120 2020-02-10 21:43:41 +00:00
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