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DAGCombiner: Don't stop finding better chain on 2 aliases 

The comment says this was stopped because it was unlikely to be
profitable. This is not true if you want to combine vector loads
with multiple components.

For a simple case that looks like

t0 = load t0 ...
t1 = load t0 ...
t2 = load t0 ...
t3 = load t0 ...

t4 = store t0:1, t0:1
  t5 = store t4, t1:0
    t6 = store t5, t2:0
	  t7 = store t6, t3:0

We want to get all of these stores onto a chain
that is a TokenFactor of these N loads. This mostly
solves the AMDGPU merge-stores.ll regressions
with -combiner-alias-analysis for merging vector
stores of vector loads.

llvm-svn: 250138
This commit is contained in:
Matt Arsenault 2015-10-13 00:49:00 +00:00
parent e69bdd10ea
commit e5d9515fb7
2 changed files with 40 additions and 26 deletions
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6
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -14298,14 +14298,12 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain,
SDValue Chain = Chains.pop_back_val();
// For TokenFactor nodes, look at each operand and only continue up the
// chain until we find two aliases. If we've seen two aliases, assume we'll
// find more and revert to original chain since the xform is unlikely to be
// profitable.
// chain until we reach the depth limit.
//
// FIXME: The depth check could be made to return the last non-aliasing
// chain we found before we hit a tokenfactor rather than the original
// chain.
if (Depth > 6 || Aliases.size() == 2) {
if (Depth > 6) {
Aliases.clear();
Aliases.push_back(OriginalChain);
return;

60
llvm/test/CodeGen/AMDGPU/merge-stores.ll
View File

@ -1,5 +1,8 @@
; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=SI -check-prefix=GCN %s
; RUN: llc -march=amdgcn -mcpu=bonaire -verify-machineinstrs < %s | FileCheck -check-prefix=SI -check-prefix=GCN %s
; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=SI -check-prefix=GCN -check-prefix=GCN-NOAA %s
; RUN: llc -march=amdgcn -mcpu=bonaire -verify-machineinstrs < %s | FileCheck -check-prefix=SI -check-prefix=GCN -check-prefix=GCN-NOAA %s
; RUN: llc -march=amdgcn -verify-machineinstrs -combiner-alias-analysis < %s | FileCheck -check-prefix=SI -check-prefix=GCN -check-prefix=GCN-AA %s
; RUN: llc -march=amdgcn -mcpu=bonaire -verify-machineinstrs -combiner-alias-analysis < %s | FileCheck -check-prefix=SI -check-prefix=GCN -check-prefix=GCN-AA %s
; Run with devices with different unaligned load restrictions.
@ -151,11 +154,15 @@ define void @merge_global_store_4_constants_f32(float addrspace(1)* %out) #0 {
; FIXME: Should be able to merge this
; GCN-LABEL: {{^}}merge_global_store_4_constants_mixed_i32_f32:
; XGCN: buffer_store_dwordx4
; GCN: buffer_store_dword
; GCN: buffer_store_dword
; GCN: buffer_store_dword
; GCN: buffer_store_dword
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-AA: buffer_store_dwordx2
; GCN-AA: buffer_store_dword v
; GCN-AA: buffer_store_dword v
; GCN: s_endpgm
define void @merge_global_store_4_constants_mixed_i32_f32(float addrspace(1)* %out) #0 {
%out.gep.1 = getelementptr float, float addrspace(1)* %out, i32 1
@ -484,11 +491,15 @@ define void @merge_global_store_4_adjacent_loads_i8_natural_align(i8 addrspace(1
; This works once AA is enabled on the subtarget
; GCN-LABEL: {{^}}merge_global_store_4_vector_elts_loads_v4i32:
; GCN: buffer_load_dwordx4 [[LOAD:v\[[0-9]+:[0-9]+\]]]
; XGCN: buffer_store_dwordx4 [[LOAD]]
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-AA: buffer_store_dwordx4 [[LOAD]]
; GCN: s_endpgm
define void @merge_global_store_4_vector_elts_loads_v4i32(i32 addrspace(1)* %out, <4 x i32> addrspace(1)* %in) #0 {
%out.gep.1 = getelementptr i32, i32 addrspace(1)* %out, i32 1
%out.gep.2 = getelementptr i32, i32 addrspace(1)* %out, i32 2
@ -606,18 +617,23 @@ define void @merge_global_store_7_constants_i32(i32 addrspace(1)* %out) {
ret void
}
; FIXME: This should do 2 dwordx4 loads
; GCN-LABEL: {{^}}merge_global_store_8_constants_i32:
; XGCN: buffer_store_dwordx4
; XGCN: buffer_store_dwordx4
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-NOAA: buffer_store_dword v
; GCN-AA: buffer_store_dwordx4
; GCN-AA: buffer_store_dwordx2
; GCN-AA: buffer_store_dwordx2
; GCN: s_endpgm
define void @merge_global_store_8_constants_i32(i32 addrspace(1)* %out) {
store i32 34, i32 addrspace(1)* %out, align 4
%idx1 = getelementptr inbounds i32, i32 addrspace(1)* %out, i64 1