slang.git/source/slang/slang-ir-eliminate-phis.cpp, branch master

Clean up Slang IR representation of undefined values (#8708)

2025-10-15T01:00:47+00:00

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` 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>

extend fiddle to allow custom lua splices in more places (#7559)

2025-07-01T19:03:41+00:00

* 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

Fix Phi elimination pass sometimes leaving broken insts in release builds (#7499)

2025-06-25T17:15:08+00:00

* Make phi elimination pass modify branches in-place * Add test and fix formatting * Avoid double removal of param insts

Move switch statement bodies to their own lines (#5493)

2024-11-05T17:47:26+00:00

* Move switch statement bodies to their own lines * format --------- Co-authored-by: Yong He

format

2024-10-29T06:49:26+00:00

* format * Minor test fixes * enable checking cpp format in ci

Report AD checkpoint contexts (#5058)

2024-09-19T03:42:07+00:00

* 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

SPIRV compiler performance fixes. (#3258)

2023-10-04T18:20:35+00:00

* SPIRV compiler performance fixes. * Cleanup. * update project files * Cleanup debug code. * Make redundancy removal non-recursive. --------- Co-authored-by: Yong He

Fix subtle corner-case with vars getting hoisted out of the loop creating unnecessary loop state (#3165)

2023-08-30T18:59:34+00:00

* 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 Co-authored-by: Yong He

Wave intrinsics. (#3164)

2023-08-29T23:43:25+00:00

* Wave intrinsics. * scalar intrinsics. --------- Co-authored-by: Yong He

Use ankerl/unordered_dense as a hashmap implementation (#3036)

2023-08-16T00:57:47+00:00

* 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