[OPT] Zero-extend unsigned 16-bit integers when bitcasting #5590
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The folding rule `BitCastScalarOrVector` was incorrectly handling bitcasting to unsigned 16-bit integers. It was simply copying the entire 32-bit word containing the 16-bit integer. This conflicts with the requirement in section 2.2.1 of the SPIR-V spec which states that unsigned numeric types with a bit width less than 32-bits must have the high-order bits set to 0. Fixes microsoft/DirectXShaderCompiler#6319.
s-perron
reviewed
Feb 17, 2024
| return const_mgr->GetConstant(type, words); | ||
| const spvtools::opt::analysis::Integer* int_type = type->AsInteger(); | ||
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| if (int_type && int_type->width() < 32 && !int_type->IsSigned()) { |
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I recently added some utility functions you can use. See constant folding rules for SConvert.
Also you might need to handle 8bit integers as well. They are allowed in Spirv.
If we are casting from unsigned to signed, do we need to sign extend?
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If we are casting from unsigned to signed, do we need to sign extend?
Ah yes we do, thanks for catching that.
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The folding rule
BitCastScalarOrVectorwas incorrectly handling bitcasting to unsigned 16-bit integers. It was simply copying the entire 32-bit word containing the 16-bit integer. This conflicts with the requirement in section 2.2.1 of the SPIR-V spec which states that unsigned numeric types with a bit width less than 32-bits must have the high-order bits set to 0.Fixes microsoft/DirectXShaderCompiler#6319.