[DAG] Recombine (binop (shift x y))

[deadalnix]

Summary

This helps address regressions in D127115 .

[lebedev.ri]

Seems fine to me?

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::visitSRL(SDNode *N) {
   //   %a = ...
   //   %b = and %a, 2
   //   %c = setcc eq %b, 0
   //   brcond %c ...
   //
   // However when after the source operand of SRL is optimized into AND, the SRL
   // itself may not be optimized further. Look for it and add the BRCOND into
   // the worklist.
+  //
+  // The also tends to happen for binary operations when SimplifyDemandedBits
+  // is involved.
+  //
+  // FIXME: This is unecessary if we process the DAG in topological order,
+  // which we plan to do. This workaround can be removed once the DAG is
+  // processed in topological order.
   if (N->hasOneUse()) {
     SDNode *Use = *N->use_begin();
-    if (Use->getOpcode() == ISD::BRCOND)
-      AddToWorklist(Use);
-    else if (Use->getOpcode() == ISD::TRUNCATE && Use->hasOneUse()) {
-      // Also look pass the truncate.
+
+    // Look pass the truncate.
+    if (Use->getOpcode() == ISD::TRUNCATE && Use->hasOneUse())
       Use = *Use->use_begin();
-      if (Use->getOpcode() == ISD::BRCOND)
-        AddToWorklist(Use);
-    }
-  }
+
+    if (Use->getOpcode() == ISD::BRCOND || Use->getOpcode() == ISD::AND ||
+        Use->getOpcode() == ISD::OR || Use->getOpcode() == ISD::XOR)
 
   // Try to transform this shift into a multiply-high if
   // it matches the appropriate pattern detected in combineShiftToMULH.
   if (SDValue MULH = combineShiftToMULH(N, DAG, TLI))
     return MULH;
 
   return SDValue();
 }

llvm/test/CodeGen/X86/bool-math.ll

 }
 
 ; Truncation hoisting must not occur with opaque constants
 ; because that can induce infinite looping.
 
 define i1 @opaque_constant(i48 %x, i48 %y) {
 ; X64-LABEL: opaque_constant:
 ; X64:       # %bb.0:
-; X64-NEXT:    movq %rsi, %rax
-; X64-NEXT:    shrq $32, %rdi
+; X64-NEXT:    movq %rdi, %rax
+; X64-NEXT:    xorq %rsi, %rax
 ; X64-NEXT:    shrq $32, %rax
-; X64-NEXT:    xorl %edi, %eax
 ; X64-NEXT:    andl $1, %eax
 ; X64-NEXT:    # kill: def $al killed $al killed $rax
 ; X64-NEXT:    retq
 ;
 ; X32-LABEL: opaque_constant:
 ; X32:       # %bb.0:
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X32-NEXT:    xorl {{[0-9]+}}(%esp), %eax