slang.git/source/slang/slang-ir-ssa.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>

Clone name hint decoration when emiting Undefined (#6415)

2025-02-25T00:25:19+00:00

* Clone name hint decoration when emiting Undefined When emiting "Undefined", we lost the information of where it was synthasized from. This prevents us from providing more helpful error messages. The issue was the when we handle "IRLoop", the inputs parameters to the Phi didn't clone the name hint decoration. This commit clones them when emiting "Undefined". * Adding more test case --------- Co-authored-by: Yong He

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

Variadic Generics Part 2: IR lowering and specialization. (#4849)

2024-08-19T04:57:24+00:00

* Variadic Generics Part 2: IR lowering and specialization. * Update design doc status. * Update design doc. * Resolve review comments.

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

Initial support for differentiating existential types (#3111)

2023-08-17T18:45:13+00:00

* Merge * WIP: Complete auto-diff logic for existential types * Revert "Add compiler option for generating representative hash" This reverts commit 13b09ef4621e73844c96d64d9c111a8ed0d45aae. * More fixes for fwd-mode AD on existential types * Add anyValueSize inference pass * Fix checking of `Differential.Differential==Differential` * In-progress: infer any-value-size for existential types * Existentials now work in forward-mode * Overhaul handling of existential AD types. Fwd-mode works, reverse-mode requires front-end changes * Reverse-mode now works on existentials * Cleanup * Remove diff rules for create existential object for now * Revert treat-as-differentiable changes * Fixes * More fixes * Cleanup * more cleanup * signed/unsigned * Revert "Cleanup" This reverts commit e4f7d71f07bb207736f90708961eeecd09a1b652. * Cleanup (again) * Remove public/export/keep-alive on null differential after AD pass * Minor fix * Update dictionary accessors * Keep export decoration * More fixes + Support for `kIROp_PackAnyValue` * Merge upstream * Update expected-failure.txt

Support implciit casted swizzled lvalue. (#3077)

2023-08-10T03:11:09+00:00

* Support implciit casted swizzled lvalue. * Fix warnings. * Fix. * fix comment. * Prefer mangled linkage name for global params. * Update tests. --------- Co-authored-by: Yong He

Fix most of the disabled warnings on gcc/clang (#2839)

2023-04-27T04:36:59+00:00