[llvm] Check for side effects when lowering target intrinsics, update NVVM ldu/ldg intrinsics with IntrWillReturn and test for DCE (PR #98968)

[Kevin McAfee via llvm-commits]

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@@ -148,3 +148,129 @@ define <2 x half> @test_ldg_v2f16(ptr addrspace(1) %ptr) {
   %val = tail call <2 x half> @llvm.nvvm.ldg.global.f.v2f16.p1(ptr addrspace(1) %ptr, i32 4)
   ret <2 x half> %val
 }
+
+; CHECK-LABEL: test_ldu_i8_dead
+define void @test_ldu_i8_dead(ptr addrspace(1) %ptr) {
+  ; CHECK-NOT: ldu.global.u8
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kalxr wrote:

Previously these weren't getting deleted before codegen since they weren't `willReturn`. With the added `IntrWillReturn` attribute they can be deleted in the middle end, so I'll get rid of these tests and make ones to reflect that.

https://github.com/llvm/llvm-project/pull/98968