[AMDGPU] SILoadStoreOptimizer: Allow merging across a swizzled access

[foad]

Summary

Swizzled accesses are not merged, but there is no particular reason not
to merge two instructions if any of the intervening instructions happens
to be a swizzled access.

This moves the check for swizzled accesses out of checkAndPrepareMerge
into collectMergeableInsts where I think it makes more sense.

[rampitec]

Is there a test with an aliasing swizzled store in between of two operations preventing the merge?

[foad]

In D118267#3273165, @rampitec wrote:

Is there a test with an aliasing swizzled store in between of two operations preventing the merge?

There is now: gfx9_tbuffer_load_merge_across_swizzled_store (see c5d2b97a6992). This patch does not affect it.

[piotr]

LGTM

llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp

bool SILoadStoreOptimizer::checkAndPrepareMerge(
   const unsigned Opc = CI.I->getOpcode();
   const InstClassEnum InstClass = getInstClass(Opc, *TII);
 
   if (InstClass == UNKNOWN) {
     return false;
   }
   const unsigned InstSubclass = getInstSubclass(Opc, *TII);
 
-  // Do not merge VMEM buffer instructions with "swizzled" bit set.
-  int Swizzled =
-      AMDGPU::getNamedOperandIdx(CI.I->getOpcode(), AMDGPU::OpName::swz);
-  if (Swizzled != -1 && CI.I->getOperand(Swizzled).getImm())
-    return false;
-
   DenseSet<Register> RegDefsToMove;
   DenseSet<Register> PhysRegUsesToMove;
   addDefsUsesToList(*CI.I, RegDefsToMove, PhysRegUsesToMove);
 
   const TargetRegisterClass *DataRC = getDataRegClass(*CI.I);
   bool IsAGPR = TRI->hasAGPRs(DataRC);
 
   MachineBasicBlock::iterator E = std::next(Paired.I);
if ((getInstClass(MBBI->getOpcode(), *TII) != InstClass) ||
       // When we match I with another DS instruction we will be moving I down
       // to the location of the matched instruction any uses of I will need to
       // be moved down as well.
       addToListsIfDependent(*MBBI, RegDefsToMove, PhysRegUsesToMove,
                             InstsToMove);
       continue;
     }
 
-    int Swizzled =
-        AMDGPU::getNamedOperandIdx(MBBI->getOpcode(), AMDGPU::OpName::swz);
-    if (Swizzled != -1 && MBBI->getOperand(Swizzled).getImm())
-      return false;
-
     // Handle a case like
     //   DS_WRITE_B32 addr, v, idx0
     //   w = DS_READ_B32 addr, idx0
     //   DS_WRITE_B32 addr, f(w), idx1
     // where the DS_READ_B32 ends up in InstsToMove and therefore prevents
     // merging of the two writes.
     if (addToListsIfDependent(*MBBI, RegDefsToMove, PhysRegUsesToMove,
                               InstsToMove))
if (MI.hasOrderedMemoryRef()) {
       ++BlockI;
       break;
     }
 
     const InstClassEnum InstClass = getInstClass(MI.getOpcode(), *TII);
     if (InstClass == UNKNOWN)
       continue;
 
+    // Do not merge VMEM buffer instructions with "swizzled" bit set.
+    int Swizzled =
+        AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::swz);
+    if (Swizzled != -1 && MI.getOperand(Swizzled).getImm())
+      continue;
+
     CombineInfo CI;
     CI.setMI(MI, *TII, *STM);
     CI.Order = Order++;
 
     if (!CI.hasMergeableAddress(*MRI))
       continue;
 
     LLVM_DEBUG(dbgs() << "Mergeable: " << MI);

llvm/test/CodeGen/AMDGPU/merge-tbuffer.mir

bb.0.entry:
     %5:sgpr_128 = REG_SEQUENCE %0:sgpr_32, %subreg.sub0, %1:sgpr_32, %subreg.sub1, %2:sgpr_32, %subreg.sub2, %3:sgpr_32, %subreg.sub3
     %7:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 4, 116, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
     %8:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 8, 116, 0, 0, 1, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
 ...
 ---
 
 
 # GFX9-LABEL: name: gfx9_tbuffer_load_merge_across_swizzle
-# GFX9: %{{[0-9]+}}:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %4, 0, 4, 116, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
 # GFX9: %{{[0-9]+}}:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %4, 0, 12, 116, 0, 0, 1, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
-# GFX9: %{{[0-9]+}}:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %4, 0, 8, 116, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
+# GFX9: %{{[0-9]+}}:vreg_64 = TBUFFER_LOAD_FORMAT_XY_OFFSET %4, 0, 4, 123, 0, 0, 0, implicit $exec :: (dereferenceable load (s64), align 1, addrspace 4)
 name: gfx9_tbuffer_load_merge_across_swizzle
 body:             |
   bb.0.entry:
     %0:sgpr_32 = COPY $sgpr0
     %1:sgpr_32 = COPY $sgpr1
     %2:sgpr_32 = COPY $sgpr2
     %3:sgpr_32 = COPY $sgpr3
     %5:sgpr_128 = REG_SEQUENCE %0:sgpr_32, %subreg.sub0, %1:sgpr_32, %subreg.sub1, %2:sgpr_32, %subreg.sub2, %3:sgpr_32, %subreg.sub3
bb.0.entry:
     %5:sgpr_128 = REG_SEQUENCE %0:sgpr_32, %subreg.sub0, %1:sgpr_32, %subreg.sub1, %2:sgpr_32, %subreg.sub2, %3:sgpr_32, %subreg.sub3
     %7:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 4, 22, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
     %8:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 8, 22, 0, 0, 1, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
 ...
 ---
 
 
 # GFX10-LABEL: name: gfx10_tbuffer_load_merge_across_swizzle
-# GFX10: %{{[0-9]+}}:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %4, 0, 4, 22, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
 # GFX10: %{{[0-9]+}}:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %4, 0, 12, 22, 0, 0, 1, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
-# GFX10: %{{[0-9]+}}:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %4, 0, 8, 22, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
+# GFX10: %{{[0-9]+}}:vreg_64 = TBUFFER_LOAD_FORMAT_XY_OFFSET %4, 0, 4, 64, 0, 0, 0, implicit $exec :: (dereferenceable load (s64), align 1, addrspace 4)
 name: gfx10_tbuffer_load_merge_across_swizzle
 body:             |
   bb.0.entry:
     %0:sgpr_32 = COPY $sgpr0
     %1:sgpr_32 = COPY $sgpr1
     %2:sgpr_32 = COPY $sgpr2
     %3:sgpr_32 = COPY $sgpr3
     %5:sgpr_128 = REG_SEQUENCE %0:sgpr_32, %subreg.sub0, %1:sgpr_32, %subreg.sub1, %2:sgpr_32, %subreg.sub2, %3:sgpr_32, %subreg.sub3
     %7:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 4, 22, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
     %8:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 12, 22, 0, 0, 1, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
     %9:vgpr_32 = TBUFFER_LOAD_FORMAT_X_OFFSET %5:sgpr_128, 0, 8, 22, 0, 0, 0, implicit $exec :: (dereferenceable load (s32), align 1, addrspace 4)
 ...
 ---