[llvm] [LV] Bundle sub reductions into VPExpressionRecipe (PR #147255)

[Sam Tebbs via llvm-commits]

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@@ -416,3 +416,146 @@ exit:
   %r.0.lcssa = phi i64 [ %rdx.next, %loop ]
   ret i64 %r.0.lcssa
 }
+
+define i32 @print_mulacc_sub(ptr %a, ptr %b) {
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SamTebbs33 wrote:

I've tried but haven't been able to come up with a test that is different in the VF chosen without these changes. I reckon that it will be easier once perhaps the AArch64 or ARM `getMulAccReductionCost` functions accept the sub version.

https://github.com/llvm/llvm-project/pull/147255