[GVN][VP] Add test case for incorrect removal of a vp.gather.

[craig.topper]

Summary

Pre-commit for D133898

[reames]

LGTM

llvm/test/Transforms/GVN/vp_gather_scatter.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -gvn -S < %s | FileCheck %s
+
+; FIXME: We shouldn't delete the second vp.gather.
+define <vscale x 8 x i32> @foo(<vscale x 8 x ptr> %p, <vscale x 8 x i32> %x, <vscale x 8 x i1> %mask, i32 %vl) {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:    [[A:%.*]] = call <vscale x 8 x i32> @llvm.vp.gather.nxv8i32.nxv8p0(<vscale x 8 x ptr> [[P:%.*]], <vscale x 8 x i1> [[MASK:%.*]], i32 [[VL:%.*]])
+; CHECK-NEXT:    [[B:%.*]] = call <vscale x 8 x i32> @llvm.vp.add.nxv8i32(<vscale x 8 x i32> [[A]], <vscale x 8 x i32> [[X:%.*]], <vscale x 8 x i1> [[MASK]], i32 [[VL]])
+; CHECK-NEXT:    call void @llvm.vp.scatter.nxv8i32.nxv8p0(<vscale x 8 x i32> [[B]], <vscale x 8 x ptr> [[P]], <vscale x 8 x i1> [[MASK]], i32 [[VL]])
+; CHECK-NEXT:    ret <vscale x 8 x i32> [[A]]
+;
+  %a = call <vscale x 8 x i32> @llvm.vp.gather.nxv8i32.nxv8p0(<vscale x 8 x ptr> %p, <vscale x 8 x i1> %mask, i32 %vl)
+  %b = call <vscale x 8 x i32> @llvm.vp.add.nxv8i32(<vscale x 8 x i32> %a, <vscale x 8 x i32> %x, <vscale x 8 x i1> %mask, i32 %vl)
+  call void @llvm.vp.scatter.nxv8i32.nxv8p0(<vscale x 8 x i32> %b, <vscale x 8 x ptr> %p, <vscale x 8 x i1> %mask, i32 %vl)
+  %c = call <vscale x 8 x i32> @llvm.vp.gather.nxv8i32.nxv8p0(<vscale x 8 x ptr> %p, <vscale x 8 x i1> %mask, i32 %vl)
+  ret <vscale x 8 x i32> %c
+}
+
+declare <vscale x 8 x i32> @llvm.vp.add.nxv8i32(<vscale x 8 x i32>, <vscale x 8 x i32>, <vscale x 8 x i1>, i32)
+declare <vscale x 8 x i32> @llvm.vp.gather.nxv8i32.nxv8p0(<vscale x 8 x ptr>, <vscale x 8 x i1>, i32)
+declare void @llvm.vp.scatter.nxv8i32.nxv8p0(<vscale x 8 x i32>, <vscale x 8 x ptr>, <vscale x 8 x i1>, i32)
+