Commit Graph

14 Commits

Author SHA1 Message Date
Stephen McGroarty
1c2cbaf569 Add GetContinueBlock to loop class.
Previously, the loop class used the terms latch and continue block
interchangeably. This patch splits the two and corrects and tests some
uses of the old uses of GetLatchBlock.
2018-05-03 14:30:41 -04:00
Toomas Remmelg
1dc2458060 Add a loop fusion pass.
This pass will look for adjacent loops that are compatible and legal to
be fused.

Loops are compatible if:

- they both have one induction variable
- they have the same upper and lower bounds
    - same initial value
    - same condition
- they have the same update step
- they are adjacent
- there are no break/continue in either of them

Fusion is legal if:

- fused loops do not have any dependencies with dependence distance
  greater than 0 that did not exist in the original loops.
- there are no function calls in the loops (could have side-effects)
- there are no barriers in the loops

It will fuse all such loops as long as the number of registers used for
the fused loop stays under the threshold defined by
max_registers_per_loop.
2018-05-01 15:40:37 -04:00
Stephen McGroarty
9a5dd6fe88 Support loop fission.
Adds support for spliting loops whose register pressure exceeds a user
provided level. This pass will split a loop into two or more loops given
that the loop is a top level loop and that spliting the loop is legal.
Control flow is left intact for dead code elimination to remove.

This pass is enabled with the --loop-fission flag to spirv-opt.
2018-05-01 15:15:10 -04:00
Victor Lomuller
0ec08c28c1 Add register liveness analysis.
For each function, the analysis determine which SSA registers are live
at the beginning of each basic block and which one are killed at
the end of the basic block.

It also includes utilities to simulate the register pressure for loop
fusion and fission.

The implementation is based on the paper "A non-iterative data-flow
algorithm for computing liveness sets in strict ssa programs" from
Boissinot et al.
2018-04-20 09:45:15 -04:00
Victor Lomuller
10e5d7cf13 Add a loop peeling pass.
For each loop in a function, the pass walks the loops from inner to outer most loop
and tries to peel loop for which a certain amount of iteration can be done before or after the loop.

To limit code growth, peeling will not happen if the growth in code size goes above a configurable threshold.
2018-04-11 15:41:29 +01:00
Alexander Johnston
61b50b3bfa ZIV and SIV loop dependence analysis.
Provides functionality to perform ZIV and SIV dependency analysis tests
between a load and store within the same loop.

Dependency tests rely on scalar analysis to prove and disprove dependencies
with regard to the loop being analysed.

Based on the 1990 paper Practical Dependence Testing by Goff, Kennedy, Tseng

Adds support for marking loops in the loop nest as IRRELEVANT.
Loops are marked IRRELEVANT if the analysed instructions contain
no induction variables for the loops, i.e. the loops induction
variable is not relevent to the dependence of the store and load.
2018-04-11 09:32:42 -04:00
Victor Lomuller
3497a94460 Add loop unswitch pass.
It moves all conditional branching and switch whose conditions are loop
invariant and uniform. Before performing the loop unswitch we check that
the loop does not contain any instruction that would prevent it
(barriers, group instructions etc.).
2018-02-27 08:52:46 -05:00
Stephen McGroarty
e354984b09 Unroller support for multiple induction variables
Support for multiple induction variables within a loop and support for
loop condition operands <= and >=.
2018-02-27 11:50:08 +00:00
Stephen McGroarty
dd8400e150 Initial support for loop unrolling.
This patch adds initial support for loop unrolling in the form of a
series of utility classes which perform the unrolling. The pass can
be run with the command spirv-opt --loop-unroll. This will unroll
loops within the module which have the unroll hint set. The unroller
imposes a number of requirements on the loops it can unroll. These are
documented in the comments for the LoopUtils::CanPerformUnroll method in
loop_utils.h. Some of the restrictions will be lifted in future patches.
2018-02-14 15:44:38 -05:00
Alexander Johnston
84ccd0b9ae Loop invariant code motion initial implementation 2018-02-08 22:55:47 -05:00
David Neto
9e19fc0f31 VS2013: LoopDescriptor LoopContainerType can't contain unique_ptr
The loop descriptor must explicitly manage the storage for contained
Loop objects.

Fixes #1262
2018-02-05 14:19:21 -05:00
Victor Lomuller
50e85c865c Add LoopUtils class to gather some loop transformation support.
This patch adds LoopUtils class to handle some loop related transformations. For now it has 2 transformations that simplifies other transformations such as loop unroll or unswitch:
 - Dedicate exit blocks: this ensure that all exit basic block
   (out-of-loop basic blocks that have a predecessor in the loop)
   have all their predecessors in the loop;
 - Loop Closed SSA (LCSSA): this ensure that all definitions in a loop are used inside the loop
   or in a phi instruction in an exit basic block.

It also adds the following capabilities:
 - Loop::IsLCSSA to test if the loop is in a LCSSA form
 - Loop::GetOrCreatePreHeaderBlock that can build a loop preheader if required;
 - New methods to allow on the fly updates of the loop descriptors.
 - New methods to allow on the fly updates of the CFG analysis.
 - Instruction::SetOperand to allow expression of the index relative to Instruction::NumOperands (to be compatible with the index returned by DefUseManager::ForEachUse)
2018-02-01 15:35:09 -05:00
Victor Lomuller
6018de81de Add LoopDescriptor as an IRContext analysis.
Move some function definitions from header to source to avoid circular definition.
2018-01-25 16:12:32 -05:00
Victor Lomuller
e8ad02f3dd Add loop descriptors and some required dominator tree extensions.
Add post-order tree iterator.

Add DominatorTreeNode extensions:
 - Add begin/end methods to do pre-order and post-order tree traversal from a given DominatorTreeNode

Add DominatorTree extensions:
  - Add begin/end methods to do pre-order and post-order tree traversal
  - Tree traversal ignore by default the pseudo entry block
  - Retrieve a DominatorTreeNode from a basic block

Add loop descriptor:
  - Add a LoopDescriptor class to register all loops in a given function.
  - Add a Loop class to describe a loop:
    - Loop parent
    - Nested loops
    - Loop depth
    - Loop header, merge, continue and preheader
    - Basic blocks that belong to the loop

Correct a bug that forced dominator tree to be constantly rebuilt.
2018-01-08 09:31:13 -05:00