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

[Matt Arsenault 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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arsenm wrote:

-NOT checks are fragile. Can you precommit generated checks? Also, why would deleting these dead intrinsics need to be done in codegen and not already done in the middle end? 

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