[PATCH] D141809: [DAG] Recombine (binop (shift x y))

[Amaury SECHET via Phabricator via llvm-commits]

deadalnix created this revision.
deadalnix added reviewers: RKSimon, craig.topper, efriedma, spatel, lebedev.ri.
Herald added subscribers: StephenFan, ecnelises, pengfei, hiraditya.
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deadalnix requested review of this revision.
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This helps address regressions in D127115 <https://reviews.llvm.org/D127115> .


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D141809

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/bool-math.ll


Index: llvm/test/CodeGen/X86/bool-math.ll
===================================================================
--- llvm/test/CodeGen/X86/bool-math.ll
+++ llvm/test/CodeGen/X86/bool-math.ll
@@ -262,10 +262,9 @@
 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
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9923,16 +9923,23 @@
   // 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)
+      AddToWorklist(Use);
   }
 
   // Try to transform this shift into a multiply-high if


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