[PATCH] D28200: [BypassSlowDivision] Do not bypass division of hash-like values

[Nikolai Bozhenov via Phabricator via llvm-commits]

n.bozhenov created this revision.
n.bozhenov added reviewers: spatel, craig.topper, bkramer, jlebar.
n.bozhenov added subscribers: llvm-commits, zansari, DavidKreitzer, aaboud, volkalexey.

Disable bypassing if one of the operands looks like a hash value. Slow
division often occurs in hashtable implementations and fast division is
never taken there because a hash value is extremely unlikely to have
enough upper bits set to zero.

A value is considered to be hash-like if it is produced by a

1. XOR operation
2. Multiplication by a constant wider than the shorter type
3. PHI instruction with at least one XOR or MUL+CONST operand.


https://reviews.llvm.org/D28200

Files:
  lib/Transforms/Utils/BypassSlowDivision.cpp
  test/CodeGen/X86/bypass-slow-division-64.ll
  test/CodeGen/X86/bypass-slow-division-fnv.ll

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