We currently build the structured order for all nodes reachable from the
loop header when unrolling a loop. However, unrolling only needs the
nodes in the loop and possibly the merge node.
To avoid needless computation, I have implemented a search that will
stop at the merge node.
Fixes#4827
* Add continue construct analysis to struct cfg analysis
Add the ability to identify which blocks are in the continue construct for a
loop, and to get functions that are called from those blocks, directly or
indirectly.
Part of https://github.com/KhronosGroup/SPIRV-Tools/issues/2912.
* Handle id overflow in the ssa rewriter.
Remove LocalSSAElim pass at the same time. It does the same thing as the SSARewrite pass. Then even share almost all of the same code.
Fixes crbug.com/997246
Added documentation to the ir context to indicates that TakeNextId()
returns 0 when the max id is reached. TODOs were added to each call
sight so that we know where we have to start to handle this case.
Handle id overflow in |SplitLoopHeader|.
Handle id overflow in |GetOrCreatePreHeaderBlock|.
Handle failure to create preheader in LICM.
Part of https://github.com/KhronosGroup/SPIRV-Tools/issues/1841.
The current implementation of merge return can create bad, but correct,
code. When it is not in a loop construct, it will insert a lot of
extra branch around code. The potentially large number of branches are
bad. At the same time, it can separate code store to variables from
its uses hiding the fact that the store dominates the load.
This hurts the later analysis because the compiler thinks that multiple
values can reach a load, when there is really only 1. This poorer
analysis leads to missed optimizations.
The solution is to create a dummy loop around the entire body of the
function, then we can break from that loop with a single branch. Also
only new merge nodes would be those at the end of loops meaning that
most analysies will not be hurt.
Remove dead code for cases that are no longer possible.
It seems like some drivers expect there the be an OpSelectionMerge
before conditional branches, even if they are not strictly needed.
So we add them.
This CL moves the files in opt/ to consistenly be under the opt::
namespace. This frees up the ir:: namespace so it can be used to make a
shared ir represenation.
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.
We are seeing shaders that have multiple returns in a functions. These
functions must get inlined for legalization purposes; however, the
inliner does not know how to inline functions that have multiple
returns.
The solution we will go with it to improve the merge return pass to
handle structured control flow.
Note that the merge return pass will assume the cfg has been cleanedup
by dead branch elimination.
Fixes#857.
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.).
Implementation of the simplification pass.
- Create pass that calls the instruction folder on each instruction and
propagate instructions that fold to a copy. This will do copy
propagation as well.
- Did not use the propagator engine because I want to modify the instruction
as we go along.
- Change folding to not allocate new instructions, but make changes in
place. This change had a big impact on compile time.
- Add simplification pass to the legalization passes in place of
insert-extract elimination.
- Added test cases for new folding rules.
- Added tests for the simplification pass
- Added a method to the CFG to apply a function to the basic blocks in
reverse post order.
Contributes to #1164.
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)
This class implements a generic value propagation algorithm based on the
conditional constant propagation algorithm proposed in
Constant propagation with conditional branches,
Wegman and Zadeck, ACM TOPLAS 13(2):181-210.
The implementation is based on
A Propagation Engine for GCC
Diego Novillo, GCC Summit 2005
http://ols.fedoraproject.org/GCC/Reprints-2005/novillo-Reprint.pdf
The purpose of this implementation is to act as a common framework for any
transformation that needs to propagate values from statements producing new
values to statements using those values.
Re-formatted the source tree with the command:
$ /usr/bin/clang-format -style=file -i \
$(find include source tools test utils -name '*.cpp' -or -name '*.h')
This required a fix to source/val/decoration.h. It was not including
spirv.h, which broke builds when the #include headers were re-ordered by
clang-format.
This class moves some of the CFG-related functionality into a new
class opt::CFG. There is some other code related to the CFG in the
inliner and in opt::LocalSingleStoreElimPass that should also be moved,
but that require more changes than this pure restructuring.
I will move those bits in a follow-up PR.
Currently, the CFG is computed every time a pass is instantiated, but
this should be later moved to the new IRContext class that @s-perron is
working on.
Other re-factoring:
- Add BasicBlock::ContinueBlockIdIfAny. Re-factored out of MergeBlockIdIfAny
- Rewrite IsLoopHeader in terms of GetLoopMergeInst.
- Run clang-format on some files.
