[llvm] [RISCV][VLOPT] Add support for checkUsers when UserMI is a Single-Width Integer Reduction (PR #120345)

[Luke Lau via llvm-commits]

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@@ -149,8 +152,11 @@ define i32 @mul_i32(<4 x i32> %a, <4 x i32> %b) {
 ; RV64-NEXT:    vslidedown.vi v10, v9, 2
 ; RV64-NEXT:    vmul.vv v9, v9, v10
 ; RV64-NEXT:    vrgather.vi v10, v8, 1
+; RV64-NEXT:    vsetivli zero, 1, e32, m1, ta, ma
 ; RV64-NEXT:    vmul.vv v8, v8, v10
+; RV64-NEXT:    vsetivli zero, 4, e32, m1, ta, ma
 ; RV64-NEXT:    vrgather.vi v10, v9, 1
+; RV64-NEXT:    vsetivli zero, 1, e32, m1, ta, ma
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lukel97 wrote:

This will be a regression on the spacemit-x60 anyway where the throughput is independent of VL.

Can the addition of the scalar moves to isVectorOpUsedAsScalarOp be split out to a separate patch, or is it definitely needed for this patch? I'm a bit confused since the title seems to imply it's only enabling reduction users

https://github.com/llvm/llvm-project/pull/120345