[llvm] [IR] Add llvm `cmul` intrinsic (PR #140301)

[Oscar Smith via llvm-commits]

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@@ -4,7 +4,7 @@
 ; RUN: llc -mtriple=riscv64 -mattr=+zbkc -verify-machineinstrs < %s \
 ; RUN:   | FileCheck %s -check-prefix=RV64ZBC-ZBKC
 
-declare i64 @llvm.riscv.clmul.i64(i64 %a, i64 %b)
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oscardssmith wrote:

This was one of the parts I'm very unsure about: Should we remove `llvm.riscv.clmul.i64` (or make it an alias somehow?) Having the `riscv` target specific version of this intrinsic seems not great, but I don't know what the best approach for maintaining simplicity and backward compatibility is.

https://github.com/llvm/llvm-project/pull/140301