[PATCH] D127115: [RFC][DAGCombine] Make sure combined nodes are added back to the worklist in topological order.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/test/CodeGen/X86/add-and-not.ll:305
+; X64-NEXT:    addq %rdi, %rax
 ; X64-NEXT:    retq
   %old = ptrtoint ptr %a to i64
----------------
```
SelectionDAG has 14 nodes:
  t0: ch,glue = EntryToken
  t2: i64,ch = CopyFromReg t0, Register:i64 %0
            t15: i32 = truncate t2
          t16: i32 = xor t15, Constant:i32<-1>
        t19: i32 = and t16, Constant:i32<1>
      t20: i64 = zero_extend t19
    t6: i64 = add t2, t20
  t9: ch,glue = CopyToReg t0, Register:i64 $rax, t6
  t10: ch = X86ISD::RET_FLAG t9, TargetConstant:i32<0>, Register:i64 $rax, t9:1
```


================
Comment at: llvm/test/CodeGen/X86/dagcombine-select.ll:217
+; CHECK-NEXT:    # kill: def $cl killed $cl killed $ecx
+; CHECK-NEXT:    shrl %cl, %eax
 ; CHECK-NEXT:    retq
----------------
Looks like the truncate means we're now failing to call foldBinOpIntoSelect before:
```
SelectionDAG has 15 nodes:
  t0: ch,glue = EntryToken
  t2: i32,ch = CopyFromReg t0, Register:i32 %0
  t3: i8 = truncate t2
          t4: i1 = truncate t2
        t7: i32 = select t4, Constant:i32<2>, Constant:i32<3>
      t9: i8 = truncate t7
    t10: i32 = shl Constant:i32<1>, t9
  t13: ch,glue = CopyToReg t0, Register:i32 $eax, t10
  t14: ch = X86ISD::RET_FLAG t13, TargetConstant:i32<0>, Register:i32 $eax, t13:1
```
becomes:
```
SelectionDAG has 14 nodes:
  t0: ch,glue = EntryToken
            t2: i32,ch = CopyFromReg t0, Register:i32 %0
          t23: i8 = truncate t2
        t25: i8 = and t23, Constant:i8<1>
      t22: i8 = xor t25, Constant:i8<3>
    t10: i32 = shl Constant:i32<1>, t22
  t13: ch,glue = CopyToReg t0, Register:i32 $eax, t10
  t14: ch = X86ISD::RET_FLAG t13, TargetConstant:i32<0>, Register:i32 $eax, t13:1
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127115/new/

https://reviews.llvm.org/D127115