[AMDGPU] Enable load clustering in the post-RA scheduler

This has a couple of benefits:
1. It can sometimes fix clusters that got broken apart when the register
   allocator inserted a copy.
2. Post-RA scheduling does not have to worry about increasing register
   pressure, which in some cases gives it more freedom to reorder
   instructions.

Testing on a collection of 10,000 graphics shaders compiled for gfx1010
showed:
- The average length of each run of one or more load instructions
  increased by about 1%.
- The number of runs of two or more load instructions increased by
  about 4%.

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -825,6 +825,7 @@ class GCNPassConfig final : public AMDGPUPassConfig {
   createPostMachineScheduler(MachineSchedContext *C) const override {
     ScheduleDAGMI *DAG = createGenericSchedPostRA(C);
     const GCNSubtarget &ST = C->MF->getSubtarget<GCNSubtarget>();
+    DAG->addMutation(createLoadClusterDAGMutation(DAG->TII, DAG->TRI));
     DAG->addMutation(ST.createFillMFMAShadowMutation(DAG->TII));
     return DAG;
   }

llvm/test/CodeGen/AMDGPU/GlobalISel/extractelement.i128.ll

@@ -185,21 +185,20 @@ define i128 @extractelement_vgpr_v4i128_vgpr_idx(<4 x i128> addrspace(1)* %ptr,
 ; GFX8-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX8-NEXT:    v_add_u32_e32 v3, vcc, 16, v0
 ; GFX8-NEXT:    v_addc_u32_e32 v4, vcc, 0, v1, vcc
-; GFX8-NEXT:    flat_load_dwordx4 v[8:11], v[0:1]
 ; GFX8-NEXT:    flat_load_dwordx4 v[4:7], v[3:4]
+; GFX8-NEXT:    flat_load_dwordx4 v[8:11], v[0:1]
 ; GFX8-NEXT:    v_lshlrev_b32_e32 v16, 1, v2
 ; GFX8-NEXT:    v_add_u32_e32 v17, vcc, 1, v16
 ; GFX8-NEXT:    v_cmp_eq_u32_e32 vcc, 1, v17
 ; GFX8-NEXT:    v_cmp_eq_u32_e64 s[4:5], 1, v16
 ; GFX8-NEXT:    v_cmp_eq_u32_e64 s[6:7], 6, v16
 ; GFX8-NEXT:    v_cmp_eq_u32_e64 s[8:9], 7, v16
-; GFX8-NEXT:    s_waitcnt vmcnt(1)
+; GFX8-NEXT:    s_waitcnt vmcnt(0)
 ; GFX8-NEXT:    v_cndmask_b32_e64 v2, v8, v10, s[4:5]
 ; GFX8-NEXT:    v_cndmask_b32_e64 v3, v9, v11, s[4:5]
 ; GFX8-NEXT:    v_cndmask_b32_e32 v8, v8, v10, vcc
 ; GFX8-NEXT:    v_cndmask_b32_e32 v9, v9, v11, vcc
 ; GFX8-NEXT:    v_cmp_eq_u32_e32 vcc, 2, v16
-; GFX8-NEXT:    s_waitcnt vmcnt(0)
 ; GFX8-NEXT:    v_cndmask_b32_e32 v2, v2, v4, vcc
 ; GFX8-NEXT:    v_cndmask_b32_e32 v3, v3, v5, vcc
 ; GFX8-NEXT:    v_cmp_eq_u32_e32 vcc, 2, v17

llvm/test/CodeGen/AMDGPU/GlobalISel/udivrem.ll

@@ -830,8 +830,8 @@ define amdgpu_kernel void @udivrem_v4i32(<4 x i32> addrspace(1)* %out0, <4 x i32
 ; GFX9-LABEL: udivrem_v4i32:
 ; GFX9:       ; %bb.0:
 ; GFX9-NEXT:    s_load_dwordx4 s[0:3], s[4:5], 0x20
-; GFX9-NEXT:    v_mov_b32_e32 v2, 0x4f7ffffe
 ; GFX9-NEXT:    s_load_dwordx4 s[8:11], s[4:5], 0x10
+; GFX9-NEXT:    v_mov_b32_e32 v2, 0x4f7ffffe
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX9-NEXT:    v_cvt_f32_u32_e32 v0, s0
 ; GFX9-NEXT:    v_cvt_f32_u32_e32 v1, s1
@@ -926,9 +926,10 @@ define amdgpu_kernel void @udivrem_v4i32(<4 x i32> addrspace(1)* %out0, <4 x i32
 ;
 ; GFX10-LABEL: udivrem_v4i32:
 ; GFX10:       ; %bb.0:
+; GFX10-NEXT:    s_clause 0x1
 ; GFX10-NEXT:    s_load_dwordx4 s[8:11], s[4:5], 0x20
-; GFX10-NEXT:    v_mov_b32_e32 v4, 0x4f7ffffe
 ; GFX10-NEXT:    s_load_dwordx4 s[0:3], s[4:5], 0x10
+; GFX10-NEXT:    v_mov_b32_e32 v4, 0x4f7ffffe
 ; GFX10-NEXT:    v_mov_b32_e32 v8, 0
 ; GFX10-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX10-NEXT:    v_cvt_f32_u32_e32 v0, s8

llvm/test/CodeGen/AMDGPU/amdgpu-codegenprepare-idiv.ll

@@ -11236,8 +11236,8 @@ define amdgpu_kernel void @sdiv_i64_pow2_shl_denom(i64 addrspace(1)* %out, i64 %
 ; GFX6-LABEL: sdiv_i64_pow2_shl_denom:
 ; GFX6:       ; %bb.0:
 ; GFX6-NEXT:    s_load_dword s4, s[0:1], 0xd
-; GFX6-NEXT:    s_mov_b64 s[2:3], 0x1000
 ; GFX6-NEXT:    s_load_dwordx4 s[8:11], s[0:1], 0x9
+; GFX6-NEXT:    s_mov_b64 s[2:3], 0x1000
 ; GFX6-NEXT:    s_mov_b32 s7, 0xf000
 ; GFX6-NEXT:    s_mov_b32 s6, -1
 ; GFX6-NEXT:    s_waitcnt lgkmcnt(0)
@@ -13358,8 +13358,8 @@ define amdgpu_kernel void @srem_i64_pow2_shl_denom(i64 addrspace(1)* %out, i64 %
 ; GFX6-LABEL: srem_i64_pow2_shl_denom:
 ; GFX6:       ; %bb.0:
 ; GFX6-NEXT:    s_load_dword s4, s[0:1], 0xd
-; GFX6-NEXT:    s_mov_b64 s[2:3], 0x1000
 ; GFX6-NEXT:    s_load_dwordx4 s[8:11], s[0:1], 0x9
+; GFX6-NEXT:    s_mov_b64 s[2:3], 0x1000
 ; GFX6-NEXT:    s_mov_b32 s7, 0xf000
 ; GFX6-NEXT:    s_mov_b32 s6, -1
 ; GFX6-NEXT:    s_waitcnt lgkmcnt(0)

llvm/test/CodeGen/AMDGPU/idiv-licm.ll

@@ -491,8 +491,8 @@ define amdgpu_kernel void @urem16_invariant_denom(i16 addrspace(1)* nocapture %a
 ; GFX9-LABEL: urem16_invariant_denom:
 ; GFX9:       ; %bb.0: ; %bb
 ; GFX9-NEXT:    s_load_dword s2, s[0:1], 0x2c
-; GFX9-NEXT:    s_mov_b32 s6, 0xffff
 ; GFX9-NEXT:    s_load_dwordx2 s[4:5], s[0:1], 0x24
+; GFX9-NEXT:    s_mov_b32 s6, 0xffff
 ; GFX9-NEXT:    v_mov_b32_e32 v1, 0
 ; GFX9-NEXT:    s_movk_i32 s8, 0x400
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)

llvm/test/CodeGen/AMDGPU/promote-constOffset-to-imm.ll

@@ -100,14 +100,14 @@ define hidden amdgpu_kernel void @clmem_read(i8 addrspace(1)*  %buffer) {
 ; GFX900:    global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 ;
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off offset:-2048
-; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off offset:-2048
-; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off offset:-2048
-; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off offset:-2048
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
+; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
+; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
+; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off offset:-2048
 ; GFX10:   global_load_dwordx2 v[{{[0-9]+:[0-9]+}}], v[{{[0-9]+:[0-9]+}}], off{{$}}
 

llvm/test/CodeGen/AMDGPU/sdiv64.ll

@@ -6,8 +6,8 @@ define amdgpu_kernel void @s_test_sdiv(i64 addrspace(1)* %out, i64 %x, i64 %y) {
 ; GCN-LABEL: s_test_sdiv:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_load_dwordx2 s[4:5], s[0:1], 0xd
-; GCN-NEXT:    v_mov_b32_e32 v7, 0
 ; GCN-NEXT:    s_load_dwordx4 s[8:11], s[0:1], 0x9
+; GCN-NEXT:    v_mov_b32_e32 v7, 0
 ; GCN-NEXT:    s_mov_b32 s7, 0xf000
 ; GCN-NEXT:    s_mov_b32 s6, -1
 ; GCN-NEXT:    s_waitcnt lgkmcnt(0)

llvm/test/CodeGen/AMDGPU/srem64.ll

@@ -6,8 +6,8 @@ define amdgpu_kernel void @s_test_srem(i64 addrspace(1)* %out, i64 %x, i64 %y) {
 ; GCN-LABEL: s_test_srem:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_load_dwordx2 s[12:13], s[0:1], 0xd
-; GCN-NEXT:    v_mov_b32_e32 v2, 0
 ; GCN-NEXT:    s_load_dwordx4 s[8:11], s[0:1], 0x9
+; GCN-NEXT:    v_mov_b32_e32 v2, 0
 ; GCN-NEXT:    s_mov_b32 s7, 0xf000
 ; GCN-NEXT:    s_mov_b32 s6, -1
 ; GCN-NEXT:    s_waitcnt lgkmcnt(0)

llvm/test/CodeGen/AMDGPU/udiv64.ll

@@ -6,8 +6,8 @@ define amdgpu_kernel void @s_test_udiv_i64(i64 addrspace(1)* %out, i64 %x, i64 %
 ; GCN-LABEL: s_test_udiv_i64:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_load_dwordx2 s[2:3], s[0:1], 0xd
-; GCN-NEXT:    v_mov_b32_e32 v2, 0
 ; GCN-NEXT:    s_load_dwordx4 s[8:11], s[0:1], 0x9
+; GCN-NEXT:    v_mov_b32_e32 v2, 0
 ; GCN-NEXT:    s_mov_b32 s7, 0xf000
 ; GCN-NEXT:    s_mov_b32 s6, -1
 ; GCN-NEXT:    s_waitcnt lgkmcnt(0)

llvm/test/CodeGen/AMDGPU/urem64.ll

@@ -6,8 +6,8 @@ define amdgpu_kernel void @s_test_urem_i64(i64 addrspace(1)* %out, i64 %x, i64 %
 ; GCN-LABEL: s_test_urem_i64:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_load_dwordx2 s[12:13], s[0:1], 0xd
-; GCN-NEXT:    v_mov_b32_e32 v2, 0
 ; GCN-NEXT:    s_load_dwordx4 s[8:11], s[0:1], 0x9
+; GCN-NEXT:    v_mov_b32_e32 v2, 0
 ; GCN-NEXT:    s_mov_b32 s7, 0xf000
 ; GCN-NEXT:    s_mov_b32 s6, -1
 ; GCN-NEXT:    s_waitcnt lgkmcnt(0)