[llvm] [LV][EVL] Generate negative strided load/store for reversed load/store (PR #123608)

[Elvis Wang via llvm-commits]

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@@ -39,16 +39,14 @@ define void @reverse_load_store(i64 %startval, ptr noalias %ptr, ptr noalias %pt
 ; IF-EVL-NEXT:    [[TMP10:%.*]] = sub i64 1, [[TMP18]]
 ; IF-EVL-NEXT:    [[TMP16:%.*]] = getelementptr i32, ptr [[TMP8]], i64 [[TMP9]]
 ; IF-EVL-NEXT:    [[TMP12:%.*]] = getelementptr i32, ptr [[TMP16]], i64 [[TMP10]]
-; IF-EVL-NEXT:    [[VP_OP_LOAD:%.*]] = call <vscale x 4 x i32> @llvm.vp.load.nxv4i32.p0(ptr align 4 [[TMP12]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP5]])
-; IF-EVL-NEXT:    [[VP_REVERSE:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vp.reverse.nxv4i32(<vscale x 4 x i32> [[VP_OP_LOAD]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP5]])
+; IF-EVL-NEXT:    [[VP_REVERSE_LOAD:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vp.strided.load.nxv4i32.p0.i32(ptr align 4 [[TMP12]], i32 -4, <vscale x 4 x i1> splat (i1 true), i32 [[TMP5]])
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ElvisWang123 wrote:

Hi @wangpc-pp , I have a question.

The original behavior is loading value from starting address ` v =  <%ptr, %ptr + 1, %ptr + 2 , ... >` and reverse the loaded vector =>  `v = <..., %ptr + 2, %ptr + 1 , %ptr>`

IIUC the behavior of `vp.strided.load()` is loading value from `%ptrs = <%ptr, %ptr + %stride, %ptr + 2 * %stride, ... >`. 
With the stride is `-1`, the loaded data will be `v = <%ptr, %ptr - 1, %ptr -2 ...>`. 

I don't think the above behaviors are equivalent.

https://github.com/llvm/llvm-project/pull/123608