[llvm] AMDGPU: share LDS budget logic and add experimental LDS buffering pass (PR #166388)

[Matt Arsenault via llvm-commits]

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+; RUN: opt -mtriple=amdgcn-amd-amdhsa -mcpu=gfx950 -passes=amdgpu-lds-buffering -S %s | FileCheck %s
+
+; Check LDS global creation
+; CHECK: @ldsbuf_test.ldsbuf = internal unnamed_addr addrspace(3) global
+
+; CHECK-LABEL: @ldsbuf_test(
+; Ensure the original direct global load is gone before the first memcpy-in
+; CHECK-NOT: load <4 x i32>, ptr addrspace(1) %p
+; LDS slot computation GEP on the function-scoped LDS global
+; CHECK: %[[SLOT:[^ ]+]] = getelementptr inbounds {{.*}}, ptr addrspace(3) @ldsbuf_test.ldsbuf, i32 0, i32 %
+; memcpy global -> LDS at the load site
+; CHECK: call void @llvm.memcpy.p3.p1.i64(ptr addrspace(3){{.*}}%[[SLOT]], ptr addrspace(1){{.*}}%p, i64 16, i1 false)
+; Ensure the original direct global store is gone between the two memcpys
+; CHECK-NOT: store <4 x i32>
+; memcpy LDS -> global at the original store site
+; CHECK: call void @llvm.memcpy.p1.p3.i64(ptr addrspace(1){{.*}}%p, ptr addrspace(3){{.*}}%[[SLOT]], i64 16, i1 false)
+
+; Minimal kernel with a single load from AS(1) used once by a
+; store back to the same pointer. Should be buffered via LDS.
+
+define amdgpu_kernel void @ldsbuf_test(ptr addrspace(1) %p) #0 {
+entry:
+  %ld = load <4 x i32>, ptr addrspace(1) %p, align 16
+  store <4 x i32> %ld, ptr addrspace(1) %p, align 16
+  ret void
+}
+
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arsenm wrote:

This needs a lot more test coverage, particularly the negative tests 

https://github.com/llvm/llvm-project/pull/166388