AMDGPU: Extend add x, (ext setcc) combine to sub

[arsenm]

Summary

This is the same as the add case, but inverts the operation type.

This avoids regressions in a future patch.

[rampitec]

AFAIR this was there with the first version of the combine, but then triggered bugs. Please run PSDB before going forward. It should work but exposed problems previously.

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

9594

What's the point of this check? Performance or correctness? It needs a comment.

[arsenm]

Add comments. This passed precheckin

[rampitec]

LGTM

[arsenm]

9d7bccab663f5e71320fb10727abcfa6c2dab046

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

SDValue SITargetLowering::performSubCombine(SDNode *N,
 
   if (VT != MVT::i32)
     return SDValue();
 
   SDLoc SL(N);
   SDValue LHS = N->getOperand(0);
   SDValue RHS = N->getOperand(1);
 
+  // sub x, zext (setcc) => subcarry x, 0, setcc
+  // sub x, sext (setcc) => addcarry x, 0, setcc
+  unsigned Opc = RHS.getOpcode();
+  switch (Opc) {
+  default: break;
+  case ISD::ZERO_EXTEND:
+  case ISD::SIGN_EXTEND:
+  case ISD::ANY_EXTEND: {
+    auto Cond = RHS.getOperand(0);
+    if (!isBoolSGPR(Cond))
+      break;
+    SDVTList VTList = DAG.getVTList(MVT::i32, MVT::i1);
+    SDValue Args[] = { LHS, DAG.getConstant(0, SL, MVT::i32), Cond };
+    Opc = (Opc == ISD::SIGN_EXTEND) ? ISD::ADDCARRY : ISD::SUBCARRY;
+    return DAG.getNode(Opc, SL, VTList, Args);
+  }
+  }
+
   if (LHS.getOpcode() == ISD::SUBCARRY) {
     // sub (subcarry x, 0, cc), y => subcarry x, y, cc
     auto C = dyn_cast<ConstantSDNode>(LHS.getOperand(1));
     if (!C || !C->isNullValue())
       return SDValue();
     SDValue Args[] = { LHS.getOperand(0), RHS, LHS.getOperand(2) };
     return DAG.getNode(ISD::SUBCARRY, SDLoc(N), LHS->getVTList(), Args);
   }

llvm/test/CodeGen/AMDGPU/combine-cond-add-sub.ll

bb:
   %cmp2 = icmp ugt i32 %x, 1
   %cmp = and i1 %cmp1, %cmp2
   %ext = zext i1 %cmp to i32
   %add = add i32 %v, %ext
   store i32 %add, i32 addrspace(1)* %gep, align 4
   ret void
 }
 
+; sub x, sext (setcc) => addcarry x, 0, setcc
+; GCN-LABEL: {{^}}cmp_sub_sext:
+; GCN: v_cmp_gt_u32_e32 vcc, v
+; GCN-NOT: vcc
+; GCN: v_addc_u32_e32 [[RESULT:v[0-9]+]], vcc, 0, v{{[0-9]+}}, vcc
+define amdgpu_kernel void @cmp_sub_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %gep = getelementptr inbounds i32, i32 addrspace(1)* %arg, i32 %x
+  %v = load i32, i32 addrspace(1)* %gep, align 4
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %add = sub i32 %v, %ext
+  store i32 %add, i32 addrspace(1)* %gep, align 4
+  ret void
+}
+
+; sub x, zext (setcc) => subcarry x, 0, setcc
+; GCN-LABEL: {{^}}cmp_sub_zext:
+; GCN: v_cmp_gt_u32_e32 vcc, v
+; GCN-NOT: vcc
+; GCN: v_subbrev_u32_e32 [[RESULT:v[0-9]+]], vcc, 0, v{{[0-9]+}}, vcc
+define amdgpu_kernel void @cmp_sub_zext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %gep = getelementptr inbounds i32, i32 addrspace(1)* %arg, i32 %x
+  %v = load i32, i32 addrspace(1)* %gep, align 4
+  %cmp = icmp ugt i32 %x, %y
+  %ext = zext i1 %cmp to i32
+  %add = sub i32 %v, %ext
+  store i32 %add, i32 addrspace(1)* %gep, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}sub_addcarry:
+; GCN: v_cmp_gt_u32_e32 vcc, v
+; GCN-NOT: vcc
+; GCN: v_addc_u32_e32 [[ADDC:v[0-9]+]], vcc, 0, v{{[0-9]+}}, vcc
+; GCN-NOT: vcc
+; GCN: v_subrev_i32_e32 [[RESULT:v[0-9]+]], vcc,
+define amdgpu_kernel void @sub_addcarry(i32 addrspace(1)* nocapture %arg, i32 %a) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %gep = getelementptr inbounds i32, i32 addrspace(1)* %arg, i32 %x
+  %v = load i32, i32 addrspace(1)* %gep, align 4
+  %cmp = icmp ugt i32 %x, %y
+  %ext = zext i1 %cmp to i32
+  %adde = add i32 %v, %ext
+  %add2 = sub i32 %adde, %a
+  store i32 %add2, i32 addrspace(1)* %gep, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}sub_subcarry:
+; GCN: v_cmp_gt_u32_e32 vcc, v
+; GCN-NOT: vcc
+; GCN: v_subb_u32_e32 [[RESULT:v[0-9]+]], vcc, v{{[0-9]+}}, v{{[0-9]+}}, vcc
+define amdgpu_kernel void @sub_subcarry(i32 addrspace(1)* nocapture %arg, i32 %a) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %gep = getelementptr inbounds i32, i32 addrspace(1)* %arg, i32 %x
+  %v = load i32, i32 addrspace(1)* %gep, align 4
+  %cmp = icmp ugt i32 %x, %y
+  %ext = zext i1 %cmp to i32
+  %adde = sub i32 %v, %ext
+  %add2 = sub i32 %adde, %a
+  store i32 %add2, i32 addrspace(1)* %gep, align 4
+  ret void
+}
+
 declare i1 @llvm.amdgcn.class.f32(float, i32) #0
 
 declare i32 @llvm.amdgcn.workitem.id.x() #0
 
 declare i32 @llvm.amdgcn.workitem.id.y() #0
 
 attributes #0 = { nounwind readnone speculatable }