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feat(legalizer): widen block arguments - #2008
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Our gMIR dialect has MLIR block arguments instead of G_PHI. This PR implements the widening legalization of it. By implementing widening legalization for block arguments, this saves one `zext` in every block, which strongly improves our loop-heavy benchmarks (about -7.5%). Unlike in LLVM, `s32` is not legal for RISC-V block arguments. LLVM makes it legal for the legalization of float values. Integers still end up in 64 bit registers. (Unlike for us, this is not done during legalization, but by storing the narrow LLT in a wider integer, which leaves the upper bits undefined just as `g_anyext` does.) llvm/llvm-project@ab0dc29 This follows #2005, #2006 and is the final part of a series to support widening legalization of block arguments. Assisted by AI
regehr
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luisacicolini
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Nov 7, 2026
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let's clarify the comment @regehr asked about and then merge |
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Our gMIR dialect has MLIR block arguments instead of G_PHI. This PR implements the widening legalization of it.
By implementing widening legalization for block arguments, this saves one
zextin every block, which strongly improves ourbenchmarks which are dependent on small loops (about -7.5%).
Unlike in LLVM,
s32is not legal for RISC-V block arguments. LLVM makes it legal for the legalization of float values. Integers still end up in 64 bit registers.(Unlike for us, this is not done during legalization, but by storing the narrow LLT in a wider integer, which leaves the upper bits undefined just as
g_anyextdoes.)llvm/llvm-project@ab0dc29
This follows #2005, #2006 and is the final part of a series to support widening legalization of block arguments.
Assisted by AI