microsoft / microsoft/DirectXShaderCompiler
Bitfields generate bad code when casted
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bug
check-in-clang
hlsl2021
- Dominant language
- C++
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- Merged PRs (30d)
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Description
Description
HLSL "Flat" casting bitfields does not properly mask bitfield members.
Steps to Reproduce
https://godbolt.org/z/MEKdTYxWM
Actual Behavior
Bit field members are read as full storage, not correctly masked, so instead of returning 3, this code returns 101057538 (0x6060402).
Environment
- DXC version: main
- Host Operating System: all
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the HLSL Flat-casting bitfield reproducer at https://godbolt.org/z/MEKdTYxWM and run it with DXC from main. Trace how the cast reads bitfield members and where masking is lost. Done means the reproduced case returns 3 rather than 101057538 on all hosts.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100