Fix edge condition in DAGCombiner to improve codegen of shift sequences.

When canonicalizing dags according to the rule
(shl (zext (shr X, c1) ), c1) ==> (zext (shl (shr X, c1), c1))

remember to add the new shl dag to the DAGCombiner worklist of nodes.
If we don't explicitly add it to the worklist of nodes to visit, we
may not trigger later on the rule that folds the shift left + logical
shift right into a AND instruction with bitmask.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192883 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a01d5636dfe8d50b2b6063837bd4a5e9f7a3d45d..0179cf181cfb643e7ecb3362cbf69821d05c7266 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3794,6 +3794,7 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
         EVT CountVT = NewOp0.getOperand(1).getValueType();
         SDValue NewSHL = DAG.getNode(ISD::SHL, SDLoc(N), NewOp0.getValueType(),
                                      NewOp0, DAG.getConstant(c2, CountVT));
+        AddToWorkList(NewSHL.getNode());
         return DAG.getNode(ISD::ZERO_EXTEND, SDLoc(N0), VT, NewSHL);
       }
     }

diff --git a/test/CodeGen/X86/dagcombine-shifts.ll b/test/CodeGen/X86/dagcombine-shifts.ll
index e5a67d7efc1ac4c89f076e49c23fcb176dee71d0..905cf052c39c5948afd2c501d89973ce89911ffb 100644 (file)
--- a/test/CodeGen/X86/dagcombine-shifts.ll
+++ b/test/CodeGen/X86/dagcombine-shifts.ll
@@ -187,6 +187,8 @@ entry:
 ; Once the add is removed, the number of uses becomes one and therefore the
 ; dags are canonicalized. After Legalization, we need to make sure that the
 ; valuetype for the shift count is legal.
+; Verify also that we correctly fold the shl-shr sequence into an 
+; AND with bitmask.
 
 define void @g(i32 %a) {
   %b = lshr i32 %a, 2
@@ -197,5 +199,11 @@ define void @g(i32 %a) {
   ret void
 }
 
+; CHECK-LABEL: @g
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: and
+; CHECK-NEXT: jmp
+
 declare void @f(i64)