Lunderberg opened a new pull request, #13724: URL: https://github.com/apache/tvm/pull/13724
Negative numerators to modulo/remainder operations are not supported by the Vulkan API. While the SPIR-V instructions [`OpSRem`](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpSRem) and [`OpSMod`](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpSMod) have identical semantics to `tir::Mod` and `tir::FloorMod`, respectively, use of either instruction within Vulkan results in undefined behavior. From the [Vulkan spec](https://registry.khronos.org/vulkan/specs/1.3/html/chap37.html#spirvenv-op-prec): > For the OpSRem and OpSMod instructions, if either operand is negative the result is undefined. > > Note: While the OpSRem and OpSMod instructions are supported by the Vulkan environment, they require non-negative values and thus do not enable additional functionality beyond what OpUMod provides. This issue was first noticed in https://github.com/apache/tvm/pull/13530, where use of integer arithmetic resulted in negative numerators. This hadn't caused issues previously, because most use of div/mod use a denominator that is a power of two. In these cases, `tir.LowerIntrin` implements floordiv and floormod using only bitwise operations. When the denominator isn't a power of two, both `tir::FloorDiv` and `tir::FloorMod` are implemented in terms of `tir::Mod`, which triggers the undefined behavior for negative numerators. This commit alters the lowering of FloorDiv/FloorMod to TruncDiv/TruncMod, in cases where the denominator is positive, the numerator is sometimes negative, and the range of the numerator is known. In these cases, the FloorDiv/FloorMod is now implemented by offsetting the numerator such that it is always positive. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
