DAGCombiner: Assume invariant load cannot alias a store

The motivation is to allow GatherAllAliases / FindBetterChain
to not give up on dependent loads of a pointer from constant memory.

This is important for AMDGPU, because most loads are pointers
derived from a load of a kernel argument from constant memory.

llvm-svn: 241948

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AMDGPU/invariant-load-no-alias-store.ll b/llvm/test/CodeGen/AMDGPU/invariant-load-no-alias-store.ll
new file mode 100644
index 00000000000..2a01a621fc4
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/invariant-load-no-alias-store.ll
@@ -0,0 +1,35 @@
+; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=GCN %s
+
+; GatherAllAliases gives up on trying to analyze cases where the
+; pointer may have been loaded from an aliased store, so make sure
+; that this works and allows moving the stores to a better chain to
+; allow them to be merged merged when it's clear the pointer is loaded
+; from constant/invariant memory.
+
+; GCN-LABEL: {{^}}test_merge_store_constant_i16_invariant_global_pointer_load:
+; GCN: buffer_load_dwordx2 [[PTR:v\[[0-9]+:[0-9]+\]]],
+; GCN: v_mov_b32_e32 [[K:v[0-9]+]], 0x1c8007b
+; GCN: buffer_store_dword [[K]], [[PTR]]
+define void @test_merge_store_constant_i16_invariant_global_pointer_load(i16 addrspace(1)* addrspace(1)* dereferenceable(4096) nonnull %in) #0 {
+  %ptr = load i16 addrspace(1)*, i16 addrspace(1)* addrspace(1)* %in, !invariant.load !0
+  %ptr.1 = getelementptr i16, i16 addrspace(1)* %ptr, i64 1
+  store i16 123, i16 addrspace(1)* %ptr, align 4
+  store i16 456, i16 addrspace(1)* %ptr.1
+  ret void
+}
+
+; GCN-LABEL: {{^}}test_merge_store_constant_i16_invariant_constant_pointer_load:
+; GCN: s_load_dwordx2 s{{\[}}[[SPTR_LO:[0-9]+]]:[[SPTR_HI:[0-9]+]]{{\]}}
+; GCN: v_mov_b32_e32 [[K:v[0-9]+]], 0x1c8007b
+; GCN: buffer_store_dword [[K]], s{{\[}}[[SPTR_LO]]:
+define void @test_merge_store_constant_i16_invariant_constant_pointer_load(i16 addrspace(1)* addrspace(2)* dereferenceable(4096) nonnull %in) #0 {
+  %ptr = load i16 addrspace(1)*, i16 addrspace(1)* addrspace(2)* %in, !invariant.load !0
+  %ptr.1 = getelementptr i16, i16 addrspace(1)* %ptr, i64 1
+  store i16 123, i16 addrspace(1)* %ptr, align 4
+  store i16 456, i16 addrspace(1)* %ptr.1
+  ret void
+}
+
+!0 = !{}
+
+attributes #0 = { nounwind }
\ No newline at end of file