[AMDGPU] Do not count implicit VGPRs in SIInsertWaitcnts (#109049)

When generating waitcounts before a use or def skip VGPRs. We never have
a real implicit VGPR operands on memory instructions, it is only for
super-reg liveness accounting.

Some other instructions (MOVRELS as an example) may have real implicit
VGPR uses though.

This is less then ideal but most of the problems observed with spills.

Author: rampitec

llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp

@@ -1752,6 +1752,14 @@ bool SIInsertWaitcnts::generateWaitcntInstBefore(MachineInstr &MI,
         const bool IsVGPR = TRI->isVectorRegister(*MRI, Op.getReg());
         for (int RegNo = Interval.first; RegNo < Interval.second; ++RegNo) {
           if (IsVGPR) {
+            // Implicit VGPR defs and uses are never a part of the memory
+            // instructions description and usually present to account for
+            // super-register liveness.
+            // TODO: Most of the other instructions also have implicit uses
+            // for the liveness accounting only.
+            if (Op.isImplicit() && MI.mayLoadOrStore())
+              continue;
+
             // RAW always needs an s_waitcnt. WAW needs an s_waitcnt unless the
             // previous write and this write are the same type of VMEM
             // instruction, in which case they are (in some architectures)

llvm/test/CodeGen/AMDGPU/GlobalISel/image-waterfall-loop-O0.ll

@@ -187,7 +187,6 @@ define <4 x float> @waterfall_loop(<8 x i32> %vgpr_srd) {
 ; CHECK-NEXT:    v_mov_b32_e32 v3, s4
 ; CHECK-NEXT:    ; kill: killed $vgpr4
 ; CHECK-NEXT:    s_xor_saveexec_b32 s4, -1
-; CHECK-NEXT:    s_waitcnt vmcnt(0)
 ; CHECK-NEXT:    buffer_load_dword v0, off, s[0:3], s32 offset:80 ; 4-byte Folded Reload
 ; CHECK-NEXT:    buffer_load_dword v2, off, s[0:3], s32 offset:84 ; 4-byte Folded Reload
 ; CHECK-NEXT:    s_mov_b32 exec_lo, s4

llvm/test/CodeGen/AMDGPU/collapse-endcf.ll

@@ -778,8 +778,8 @@ define amdgpu_kernel void @nested_if_else_if(ptr addrspace(1) nocapture %arg) {
 ; GCN-O0-NEXT:    s_mov_b64 exec, s[0:1]
 ; GCN-O0-NEXT:    s_cbranch_execz .LBB3_7
 ; GCN-O0-NEXT:  ; %bb.3: ; %bb.inner.then
-; GCN-O0-NEXT:    s_waitcnt expcnt(1)
 ; GCN-O0-NEXT:    buffer_load_dword v1, off, s[12:15], 0 offset:4 ; 4-byte Folded Reload
+; GCN-O0-NEXT:    s_waitcnt expcnt(1)
 ; GCN-O0-NEXT:    buffer_load_dword v2, off, s[12:15], 0 offset:8 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    s_mov_b32 s0, 0xf000
 ; GCN-O0-NEXT:    s_mov_b32 s2, 0
@@ -824,8 +824,8 @@ define amdgpu_kernel void @nested_if_else_if(ptr addrspace(1) nocapture %arg) {
 ; GCN-O0-NEXT:    s_mov_b64 exec, s[0:1]
 ; GCN-O0-NEXT:    s_cbranch_execz .LBB3_6
 ; GCN-O0-NEXT:  ; %bb.5: ; %bb.inner.then2
-; GCN-O0-NEXT:    s_waitcnt expcnt(1)
 ; GCN-O0-NEXT:    buffer_load_dword v1, off, s[12:15], 0 offset:4 ; 4-byte Folded Reload
+; GCN-O0-NEXT:    s_waitcnt expcnt(1)
 ; GCN-O0-NEXT:    buffer_load_dword v2, off, s[12:15], 0 offset:8 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    s_mov_b32 s0, 0xf000
 ; GCN-O0-NEXT:    s_mov_b32 s2, 0
@@ -1242,10 +1242,13 @@ define void @scc_liveness(i32 %arg) local_unnamed_addr #0 {
 ; GCN-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:12 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    buffer_load_dword v2, off, s[0:3], s32 offset:16 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    buffer_load_dword v3, off, s[0:3], s32 offset:20 ; 4-byte Folded Reload
-; GCN-O0-NEXT:    s_waitcnt vmcnt(0)
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v0, off, s[0:3], s32 offset:40 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v1, off, s[0:3], s32 offset:44 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v2, off, s[0:3], s32 offset:48 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v3, off, s[0:3], s32 offset:52 ; 4-byte Folded Spill
 ; GCN-O0-NEXT:    s_branch .LBB5_7
 ; GCN-O0-NEXT:  .LBB5_6: ; %Flow
@@ -1263,10 +1266,13 @@ define void @scc_liveness(i32 %arg) local_unnamed_addr #0 {
 ; GCN-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:28 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    buffer_load_dword v2, off, s[0:3], s32 offset:32 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    buffer_load_dword v3, off, s[0:3], s32 offset:36 ; 4-byte Folded Reload
-; GCN-O0-NEXT:    s_waitcnt vmcnt(0)
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v0, off, s[0:3], s32 offset:8 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v1, off, s[0:3], s32 offset:12 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v2, off, s[0:3], s32 offset:16 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(3)
 ; GCN-O0-NEXT:    buffer_store_dword v3, off, s[0:3], s32 offset:20 ; 4-byte Folded Spill
 ; GCN-O0-NEXT:    s_branch .LBB5_5
 ; GCN-O0-NEXT:  .LBB5_7: ; %bb10
@@ -1336,10 +1342,13 @@ define void @scc_liveness(i32 %arg) local_unnamed_addr #0 {
 ; GCN-O0-NEXT:    s_or_saveexec_b64 s[14:15], -1
 ; GCN-O0-NEXT:    buffer_store_dword v4, off, s[0:3], s32 ; 4-byte Folded Spill
 ; GCN-O0-NEXT:    s_mov_b64 exec, s[14:15]
-; GCN-O0-NEXT:    s_waitcnt vmcnt(1)
+; GCN-O0-NEXT:    s_waitcnt vmcnt(4)
 ; GCN-O0-NEXT:    buffer_store_dword v0, off, s[0:3], s32 offset:56 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(4)
 ; GCN-O0-NEXT:    buffer_store_dword v1, off, s[0:3], s32 offset:60 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(4)
 ; GCN-O0-NEXT:    buffer_store_dword v2, off, s[0:3], s32 offset:64 ; 4-byte Folded Spill
+; GCN-O0-NEXT:    s_waitcnt vmcnt(4)
 ; GCN-O0-NEXT:    buffer_store_dword v3, off, s[0:3], s32 offset:68 ; 4-byte Folded Spill
 ; GCN-O0-NEXT:    s_andn2_b64 exec, exec, s[4:5]
 ; GCN-O0-NEXT:    s_cbranch_execnz .LBB5_1
@@ -1356,9 +1365,11 @@ define void @scc_liveness(i32 %arg) local_unnamed_addr #0 {
 ; GCN-O0-NEXT:    s_or_saveexec_b64 s[14:15], -1
 ; GCN-O0-NEXT:    buffer_load_dword v0, off, s[0:3], s32 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    s_mov_b64 exec, s[14:15]
-; GCN-O0-NEXT:    s_waitcnt expcnt(0)
+; GCN-O0-NEXT:    s_waitcnt expcnt(2)
 ; GCN-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:56 ; 4-byte Folded Reload
+; GCN-O0-NEXT:    s_waitcnt expcnt(1)
 ; GCN-O0-NEXT:    buffer_load_dword v2, off, s[0:3], s32 offset:60 ; 4-byte Folded Reload
+; GCN-O0-NEXT:    s_waitcnt expcnt(0)
 ; GCN-O0-NEXT:    buffer_load_dword v3, off, s[0:3], s32 offset:64 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    buffer_load_dword v4, off, s[0:3], s32 offset:68 ; 4-byte Folded Reload
 ; GCN-O0-NEXT:    s_waitcnt vmcnt(0)