d7eb619299
Summary: We add the precise cache sizes and associativity for the following Intel architectures: - Penry - Nehalem - Westmere - Sandy Bridge - Ivy Bridge - Haswell - Broadwell - Skylake - Kabylake Polly uses since several months a performance model for BLAS computations that derives optimal cache and register tile sizes from cache and latency information (based on ideas from "Analytical Modeling Is Enough for High-Performance BLIS", by Tze Meng Low published at TOMS 2016). While bootstrapping this model, these target values have been kept in Polly. However, as our implementation is now rather mature, it seems time to teach LLVM itself about cache sizes. Interestingly, L1 and L2 cache sizes are pretty constant across micro-architectures, hence a set of architecture specific default values seems like a good start. They can be expanded to more target specific values, in case certain newer architectures require different values. For now a set of Intel architectures are provided. Just as a little teaser, for a simple gemm kernel this model allows us to improve performance from 1.2s to 0.27s. For gemm kernels with less optimal memory layouts even larger speedups can be reported. Reviewers: Meinersbur, bollu, singam-sanjay, hfinkel, gareevroman, fhahn, sebpop, efriedma, asb Reviewed By: fhahn, asb Subscribers: lsaba, asb, pollydev, llvm-commits Differential Revision: https://reviews.llvm.org/D37051 llvm-svn: 311647
Analysis Opportunities:
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In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
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In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
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