Commit Graph

5 Commits

Author SHA1 Message Date
Arthur Eubanks 84a8ca1e6c [NewPM] Pin -lazy-branch-prob and -lazy-block-freq tests to legacy PM
NPM passes just use the normal versions of these analyses instead.
Also pin any tests with -analyze to legacy PM.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D87857
2020-09-21 17:51:46 -07:00
Fangrui Song 502a77f125 Migrate function attribute "no-frame-pointer-elim" to "frame-pointer"="all" as cleanups after D56351 2019-12-24 15:57:33 -08:00
Xinliang David Li 6e5dd41481 [PM] Port Branch Probability Analysis pass to the new pass manager.
Differential Revision: http://reviews.llvm.org/D19839

llvm-svn: 268601
2016-05-05 02:59:57 +00:00
Cong Hou 15ea016346 Use fixed-point representation for BranchProbability.
BranchProbability now is represented by its numerator and denominator in uint32_t type. This patch changes this representation into a fixed point that is represented by the numerator in uint32_t type and a constant denominator 1<<31. This is quite similar to the representation of BlockMass in BlockFrequencyInfoImpl.h. There are several pros and cons of this change:

Pros:

1. It uses only a half space of the current one.
2. Some operations are much faster like plus, subtraction, comparison, and scaling by an integer.

Cons:

1. Constructing a probability using arbitrary numerator and denominator needs additional calculations.
2. It is a little less precise than before as we use a fixed denominator. For example, 1 - 1/3 may not be exactly identical to 1 / 3 (this will lead to many BranchProbability unit test failures). This should not matter when we only use it for branch probability. If we use it like a rational value for some precise calculations we may need another construct like ValueRatio.

One important reason for this change is that we propose to store branch probabilities instead of edge weights in MachineBasicBlock. We also want clients to use probability instead of weight when adding successors to a MBB. The current BranchProbability has more space which may be a concern.

Differential revision: http://reviews.llvm.org/D12603

llvm-svn: 248633
2015-09-25 23:09:59 +00:00
Diego Novillo de5b8016ab Fix information loss in branch probability computation.
Summary:
This addresses PR 22718. When branch weights are too large, they were
being clamped to the range [1, MaxWeightForBB]. But this clamping is
only applied to edges that go outside the range, so it distorts the
relative branch probabilities.

This patch changes the weight calculation to scale every branch so the
relative probabilities are preserved. The scaling is done differently
now. First, all the branch weights are added up, and if the sum exceeds
32 bits, it computes an integer scale to bring all the weights within
the range.

The patch fixes an existing test that had slightly wrong branch
probabilities due to the previous clamping. It now gets branch weights
scaled accordingly.

Reviewers: dexonsmith

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9442

llvm-svn: 236750
2015-05-07 17:22:06 +00:00