Comments

Author: Pierre-vh

llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp

@@ -792,6 +792,8 @@ class WaitcntBrackets {
       auto STy = getSgprScoresIdx(T);
       for (MCRegUnit RU : regunits(Reg))
         SGPRs[RU].Scores[STy] = Val;
+    } else {
+      llvm_unreachable("Register cannot be tracked/unknown register!");
     }
   }
 
@@ -815,7 +817,7 @@ class WaitcntBrackets {
   // The score tracking logic is fragmented as follows:
   // - VMem: VGPR RegUnits and LDS DMA IDs, see the VMEMID encoding.
   // - SGPRs: SGPR RegUnits
-  // - SCC
+  // - SCC: Non-allocatable and not general purpose: not a SGPR.
   //
   // For the VMem case, if the key is within the range of LDS DMA IDs,
   // then the corresponding index into the `LDSDMAStores` vector below is:

llvm/test/CodeGen/AMDGPU/lds-dma-waits.ll

@@ -155,8 +155,6 @@ main_body:
   ret void
 }
 
-; There are 8 pseudo registers defined to track LDS DMA dependencies.
-
 define amdgpu_kernel void @buffer_load_lds_dword_10_arrays(<4 x i32> %rsrc, i32 %i1, i32 %i2, i32 %i3, i32 %i4, i32 %i5, i32 %i6, i32 %i7, i32 %i8, i32 %i9, ptr addrspace(1) %out) {
 ; GFX9-LABEL: buffer_load_lds_dword_10_arrays:
 ; GFX9:       ; %bb.0: ; %main_body
@@ -222,8 +220,10 @@ define amdgpu_kernel void @buffer_load_lds_dword_10_arrays(<4 x i32> %rsrc, i32
 ; GFX9-NEXT:    s_waitcnt vmcnt(2)
 ; GFX9-NEXT:    ds_read_b32 v7, v9 offset:1792
 ; GFX9-NEXT:    ; wave barrier
+; GFX9-NEXT:    s_waitcnt vmcnt(1)
 ; GFX9-NEXT:    ds_read_b32 v8, v9 offset:2048
 ; GFX9-NEXT:    ; wave barrier
+; GFX9-NEXT:    s_waitcnt vmcnt(0)
 ; GFX9-NEXT:    ds_read_b32 v9, v9 offset:2304
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX9-NEXT:    global_store_dwordx4 v10, v[0:3], s[0:1]
@@ -287,8 +287,10 @@ define amdgpu_kernel void @buffer_load_lds_dword_10_arrays(<4 x i32> %rsrc, i32
 ; GFX10-NEXT:    s_waitcnt vmcnt(2)
 ; GFX10-NEXT:    ds_read_b32 v7, v9 offset:1792
 ; GFX10-NEXT:    ; wave barrier
+; GFX10-NEXT:    s_waitcnt vmcnt(1)
 ; GFX10-NEXT:    ds_read_b32 v8, v9 offset:2048
 ; GFX10-NEXT:    ; wave barrier
+; GFX10-NEXT:    s_waitcnt vmcnt(0)
 ; GFX10-NEXT:    ds_read_b32 v9, v9 offset:2304
 ; GFX10-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX10-NEXT:    global_store_dwordx4 v10, v[0:3], s[0:1]