| Commit message (Collapse) | Author | Age |
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Prior to this change, the Slang IR used a single opcode
(`kIROp_Undefined`) to encode all cases of undefined values. The
particular motivation for this change was a need to distinguish those
undefined values that represent a load from an uninitialized memory
location versus other sorts of undefined values. If transforming a
variable into SSA form results in `undefined` values in cases where the
a `load` was executed without a prior `store`, that represents an error
on the programmer's part, and should be diagnosed. However, other cases
of undefined values can arise during program transformation and
optimization, and should not typically result in diagnostics being
emitted.
While it was not the original motivation for this change, it is also
worth noting that the LLVM project has transitioned from initially using
only a single `undef` instruction to having a more nuanced model, and
the same factors that motivated their shift also apply to the Slang IR.
Counter-intuitively, the semantics of undefined values actually need to
be carefully defined.
Concretely, this change splits the pre-existing `undefined` opcode into
two sub-cases:
- `kIROp_LoadFromUninitializedMemory`, to represent the case of loading
from a memory location (such as a local variable) that has not been
initialized.
- `kIROp_Poison`, corresponding to the LLVM `poison` value.
Our poison instruction is intended to have semantics comparable to
LLVM's equivalent. Conceptually, any operation that is invoked with a
poison value as input will (with a few exceptions) produce a poison
value as output. One can think of the behavior of `poison` as similar to
how not-a-number values propagate in floating-point computations: by
default they "infect" the result of any computation they are involved
in. This semantic choice helps to ensure that many optimizations end up
being correct in the presence of undefined values, even if they did not
specifically account for them.
The `kIROp_LoadFromUninitializedMemory` case is comparable to the
combination of `freeze` and `undef` in LLVM. An LLVM `undef` value has
semantics that allow *each* use of that value to be replaced with a
*different* arbitrary value; these semantics cause many optimizations to
only be correct in the absence of undefined values. An LLVM `freeze`
instruction can take an undefined value as input, and produces a single
value that is still arbitrary, but must be consistent across all uses.
The latter semantics are what we want, since a given `load` from an
uninitialized memory location will yield an arbitrary-but-fixed value.
Note that we intentionally do not have a direct analogue to LLVM's
`undef` instruction, because of the way that `undef` causes so many
complications when trying to write optimizations.
We also do not add a `kIROp_Freeze` instruction in this change, but that
is simply because we currently have no need for it.
Existing code that was creating `IRUndefined` values has been updated to
create either `IRPoison` or `IRLoadFromUninitializedMemory` values, as
appropriate to the use case. Code that was checking for the
`kIROp_Undefined` opcode has been updated to either check for both of
the new opcodes (in the case of `switch` statements), or to use
`as<IRUndefined>` to perform a dynamic cast to the common base type of
the two new instructions.
Note that this change does not alter the way that instructions
representing undefined values are typically emitted as ordinary
instructions in the block that produces an undefined value. While
emitting `IRLoadFromUninitializedMemory` as an ordinary instruction is
exactly what we want, the `IRPoison` case would actually be better
represented in Slang IR as a "hoistable" instruction, so that there
would only be a singular `poison` value of each type. Changing
`IRPoison` to be hoistable would be a good follow-up change, but might
run into more challenges depending on what assumptions (if any) the
codebase is making about where undefined values get emitted.
---------
Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>
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* Add fkYAML submodule
* Generate slang-ir-inst-defs.h from slang-ir-inst-defs.yaml
* generate ir-inst-defs.h
* neaten things
* neaten inst def parser
* add rapidyaml submodule
* remove fkyaml
* remove fkyaml submodule
* remove use of ir-inst-defs.h
* format and warnings
* fix wasm build
* tidy
* remove rapidyaml
* Extend fiddle to allow custom splices in more places
* Use lua to describe ir insts
* fix
* neaten
* neaten
* neaten
* spelling
* neaten
* comment comment out assert
* merge
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(#7499)
* Make phi elimination pass modify branches in-place
* Add test and fix formatting
* Avoid double removal of param insts
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* Move switch statement bodies to their own lines
* format
---------
Co-authored-by: Yong He <yonghe@outlook.com>
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* format
* Minor test fixes
* enable checking cpp format in ci
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* Transferring source locations when creating phi instructions
* Tracking for simple variables
* Deriving source locations for loop counters
* Printing checkpoint structure breakdown
* More readable output format
* Special behavior for loop counters
* Writing report to file
* Add slangc option to enable checkpoint reports
* Display types of checkpointed fields
* Message in case there are no checkpointing contexts
* Catch source locations for function calls
* Source cleanup
* Fix compilation warnings
* Remove stray dump()
* Provide the report through diagnostic notes
* Add missing path for sourceLoc during unzip pass
* Add tests for reporting intermediates
* Include more transfer cases for source locations
* Fix ordering in address elimination
* Fill in more holes with source location transfer
* Remove debugging line
* Reverting changes to diagnostic sink
* Simplify address elimination using source location RAII contexts
* Eliminating manual source loc transfers in forward transcription
* Fix local var adaptation to use RAII location setter
* Simplify primal hoisting logic for source location transfer
* Simplify unzipping with RAII location scopes
* Simplify transpose logic
* Cleaning up for rev.cpp
* Reverting spacing changes
* Fix mistake with source loc RAII instantiation
* Fix formatting issues
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* SPIRV compiler performance fixes.
* Cleanup.
* update project files
* Cleanup debug code.
* Make redundancy removal non-recursive.
---------
Co-authored-by: Yong He <yhe@nvidia.com>
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unnecessary loop state (#3165)
* Extend the unit tests for MxLayeredMaterial
* Add breaking loop test
* Fix subtle corner-case with vars getting hoisted out of the loop creating unnecessary loop state
* remove whitespace changes
* Create loop-init.slang.expected.txt
* Add filecheck tests to ensure correct loop state
* Update comment
---------
Co-authored-by: winmad <winmad.wlf@gmail.com>
Co-authored-by: Yong He <yonghe@outlook.com>
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* Wave intrinsics.
* scalar intrinsics.
---------
Co-authored-by: Yong He <yhe@nvidia.com>
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* Correct namespace for getClockFrequency
* missing const
* Add missing assignment operator
* Remove unused variables
* Return correct modified variable
* Use stable hash code for file system identity
* terse static_assert
* Structured binding for map iteration
* Make (==) and getHashCode const on many structs
* Add ConstIterator for LinkedList
* Replace uses of ItemProxy::getValue with Dictionary::at
* Extract list of loads from gradientsMap before updating it
* Const correctness in type layout
* Add unordered_dense hashmap submodule
* Use wyhash or getHashCode in slang-hash.h
* refactor slang-hash.h
* Use ankerl/unordered_dense as a hashmap implementation
Notable changes:
- The subscript operator returns a reference directly to the value,
rather than a lazy ItemProxy (pair of dict pointer and key)
slang-profile time (95% over 10 runs):
- Before: 6.3913906 (±0.0746)
- After: 5.9276123 (±0.0964)
* 64 bit hash for strings
So they have the same hash as char buffers with the same contents
* Narrowing warnings for gcc to match msvc
* revert back to c++17
* Correct c++ version for msvc
* Use path to unordered_dense which keeps tests happy
* Do not assign to and read from map in same expression
* Remove redundant map operations in primal-hoist
* Split out stable hash functions into slang-stable-hash.h
* 64 bit hash by default
* regenerate vs projects
* Correct return type from HashSetBase::getCount()
* correct width for call to Dictionary::reserve
* Use stable hash for obfuscated module ids
* Signed int for reserve
* clearer variable naming
* Parameterize Dictionary on hash and equality functors
* Allow heterogenous lookup for Dictionary
* missing const
* Use set over operator[] in some places
* Remove unused function
* s/at/getValue
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* #include an absolute path didn't work - because paths were taken to always be relative.
* WIP lowerCamel Dictionary.
* WIP more lowerCamel fixes for Dictionary.
* Add/Remove/Clear
* GetValue/Contains
* Fix tabs in dictionary.
Count -> getCount
* Fix fields with caps.
* Key -> key
Value -> value
Use m_ for members where appropriate.
Use lowerCamel in linked list.
* Some small fixes/improvements to Dictionary.
* Kick CI.
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Co-authored-by: Yong He <yhe@nvidia.com>
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* Register allocation during phi elimination.
* Enhance the test case.
* Cleanup line breaks in test case.
* remove unncessary line break changes.
* More cleanups.
---------
Co-authored-by: Yong He <yhe@nvidia.com>
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* Support multi-level break.
* Single return.
* Add test for inlining `void` return-type functions.
Co-authored-by: Yong He <yhe@nvidia.com>
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* #include an absolute path didn't work - because paths were taken to always be relative.
* Remove the need for LivenessLocation.
* Use LivenessMode.
* Fix some comments.
Co-authored-by: Yong He <yonghe@outlook.com>
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* #include an absolute path didn't work - because paths were taken to always be relative.
* Refactor Liveness pass, such that locations can be found independently of setting up ranges.
* Refactor around different stages of liveness span analysis.
* WIP Take into account PHI temporaries in liveness tracking.
* WIP First pass of PHI liveness refactor.
* Add BlockIndex.
* WIP Refactor phi liveness around inst runs.
* More improvements around liveness tracking.
* Bug fixes.
Special handling to not add multiple ends, at starts of blocks and after accesses.
* Fix test output.
* Use IRInsertLoc to track insertion point.
* Liveness markers don't have side effects.
* Fix typo in liveness test.
* Small improvements around setting SuccessorResult.
* Fix memory issue around reallocation and RAIIStackArray.
Update test output.
* Update test output for liveness.slang.
* Fix typo in SuccessorResult blockIndex.
* Small tidy up.
* Handle the root start block, correctly scoping the run.
* Split BlockInfo into 'Root' and 'Function'.
Store successors as BlockIndices.
* Tidy up around liveness tracking.
* Add head/tail support to ArrayViews.
Use Count where appropriate.
Use head/tail in liveness impl.
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* Use IR pass to eliminate phi nodes
"Phi nodes" are one of the key contrivances that makes SSA (Static
Single Assignment) form work. Because SSA is so great for compiler
IRs, we kind of need to deal with phi nodes, but they also get in
the way because they don't have a direct analog in most lower-level
machine ISAs or execution models, nor in most of the high-level
languages a transpiler wants to emit. As a result a compiler like
ours needs to be able to eliminate the phi nodes from a program as
part of generating output code.
(For any clever people noting that SPIR-V supports phi nodes
directly: yes, it does. It doesn't need to and it probably *shouldn't*.
Anybody involved in the decision-making knows my reasoning, and
anybody else should feel free to ask me if they want the lecture.
Anyway...)
The basic idea of elimiating phi nodes is simple enough. We replace
each phi node with a temporary variable. Uses of the phi use values
loaded from the temporary. The operation of the phi itself
(assigning a value based on the branch taken) amounts to an assignment
into the temporary.
Previously, the Slang compiler dealt with phi nodes very late in
the process of generating code: in the middle of emitting strings
of source code in a high-level language like HLSL or GLSL. Doing the
work that late in compilation has two big drawbacks:
1. Our ability to emit clean and/or optimal code is limited because
we may not be able to make certain changes to the IR, or because we
cannot make use of additional information like a dominator tree that
might be available at other points in compilation.
2. Any other IR passes that relate to temporary variables won't be
able to see the variables that we generate for phi nodes. This could
raise issues with correctness (e.g., if we want to compute live-range
information for *all* temporary variables), or performance (we have no
way to run additional IR optimization passes after phis are eliminated).
This change addresses these problems by making the elimination of
phi nodes an explicit IR pass. Additional optimizations can easily be
run after this pass (although we'd need to be careful not to run
passes that could end up introducing new phis). The pass makes use
of the information available to it to try to produce code that will
emit to "clean" HLSL/GLSL.
The core of the pass is in `slang-ir-eliminate-phis.cpp`, and is
heavily commented, so I won't describe the approach in detail here.
There are two related issues that came up, though:
First, it turned out that our emit logic for local variables (`IRVar`
instructions) wasn't using the function we'd defined named `emitVar()`.
One worrying consequence of that oversight was that the `precise`
modifier would impact generated HLSL/GLSL for variables that turned
into SSA values (including phi nodes), but *not* for local variables
that had not been SSA'd (or that had been SSA'd and then de-SSA'd).
This change also fixes that bug; it is unclear how widespread the
impact of the original issue might be.
Second, generating explicit IR temporaries for phi nodes exposed a
pre-existing bug in the `slang-ir-restructure-scoping` pass. That pass
basically detects cases where we have an instruction `I` with a use
`U` such that the use follows the rules of SSA form ("def dominates
use," meaning `I` dominations `U`), but does not follow the more
restrictive scoping rules of high-level-language output (where a value
computed "inside" a loop is not automatically visible to code outside
the loop just because it dominates that code). That pass did not
correctly account for the case where `I` was a temporary variable.
It seems that case could not arise before now because we didn't have
any passes that would move `var`, `load`, or `store` operations out
of the basic block they started in. The fix for that pass was relatively
simple, and will make the whole thing more robust in case we add more
aggressive optimizations later.
* fixup: expected test output
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