Fix a miscompile that occurs when reading a matrix contained in a struct with no sibling fields#8568
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…uct with no sibling fields. The expected behavior is that each load instruction is at a 4 byte offset, but observed behavior is that Loads are always at 0 offset. This was introduced in commit 909c552 (merged 2025-03-17), and it's observable regressed between the releases v1.8.2502 and v1.8.2505. The regression was tested as still live in v1.10.2605.24 and current HEAD. This change adds a test that reproduces the problem. ClangHLSLTests shows 2 failures with this test pre-patch and 0 failures after the patch.
Contributor
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✅ With the latest revision this PR passed the C/C++ code formatter. |
Author
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@microsoft-github-policy-service agree |
Author
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Just FYI, I'm really not familiar with the code in DXC. I have high confidence in the added test, and that this was a legitimate bug and when the regression occurred. I don't have confidence that this is the "best" fix and am very happy for someone who is familiar with this area to determine the right way to fix it. (But it does resolve the added test without breaking other tests.) |
Author
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I put a godbolt repro here: https://godbolt.org/z/bG5reh3rh |
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Fix a miscompile that occurs when reading a matrix contained in a struct with no sibling fields. The expected behavior is that each load instruction is at a 4 byte offset, but observed behavior is that Loads are always at 0 offset.
This was introduced in commit 909c552 (merged 2025-03-17), and it's observable regressed between the releases v1.8.2502 and v1.8.2505. The regression was tested as still live in v1.10.2605.24 and current HEAD.
This change adds a test that reproduces the problem. ClangHLSLTests shows 2 failures with this test pre-patch and 0 failures after the patch.