[all-commits] [llvm/llvm-project] a415b7: [WebAssembly] Add more lowerings for wide-arithmet...

[Alex Crichton via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a415b7f86e8c50e4e789d4651f3231d5078c5859
      https://github.com/llvm/llvm-project/commit/a415b7f86e8c50e4e789d4651f3231d5078c5859
  Author: Alex Crichton <alex at alexcrichton.com>
  Date:   2025-03-31 (Mon, 31 Mar 2025)

  Changed paths:
    M llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h
    M llvm/test/CodeGen/WebAssembly/wide-arithmetic.ll

  Log Message:
  -----------
  [WebAssembly] Add more lowerings for wide-arithmetic (#132430)

This commit is the result of investigation and discussion on
WebAssembly/wide-arithmetic#6 where alternatives to the `i64.add128`
instruction were discussed but ultimately deferred to a future proposal.
In spite of this though I wanted to apply a few changes to the LLVM
backend here with `wide-arithmetic` enabled for a few minor changes:

* A lowering for the `ISD::UADDO` node is added which uses `add128`
where the upper bits of the two operands are constant zeros and the
result of the 128-bit addition is the result of the overflowing
addition.
* The high bits of a `I64_ADD128` node are now flagged as "known zero"
if the upper bits of the inputs are also zero, assisting this `UADDO`
lowering to ensure the backend knows that the carry result is a 1-bit
result.

A few tests were then added to showcase various lowerings for various
operations that can be done with wide-arithmetic. They don't all
optimize super well at this time but I wanted to add them as a reference
here regardless to have them on-hand for future evaluations if
necessary.



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