[SDAG] Now that we have a way to communicate the exact bit on sdiv use it to simplify sdiv by a constant.

We had a hack in SDAGBuilder in place to work around this but now we
can avoid that. Call BuildExactSDIV from BuildSDIV so DAGCombiner can
perform this trick automatically.

The added check in DAGCombiner is necessary to prevent exact sdiv by pow2
from regressing as the target-specific pow2 lowering is not aware of
exact bits yet.

This is mostly covered by existing tests. One side effect is that we
get the better lowering for exact vector sdivs now too :)

llvm-svn: 240891

1 files changed, 5 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 329c1706171..85b2d5f62ff 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2238,17 +2238,11 @@ void SelectionDAGBuilder::visitSDiv(const User &I) {
   SDValue Op1 = getValue(I.getOperand(0));
   SDValue Op2 = getValue(I.getOperand(1));
 
-  // Turn exact SDivs into multiplications.
-  // FIXME: This should be in DAGCombiner, but it doesn't have access to the
-  // exact bit.
-  if (isa<BinaryOperator>(&I) && cast<BinaryOperator>(&I)->isExact() &&
-      !isa<ConstantSDNode>(Op1) &&
-      isa<ConstantSDNode>(Op2) && !cast<ConstantSDNode>(Op2)->isNullValue())
-    setValue(&I, DAG.getTargetLoweringInfo()
-                     .BuildExactSDIV(Op1, Op2, getCurSDLoc(), DAG));
-  else
-    setValue(&I, DAG.getNode(ISD::SDIV, getCurSDLoc(), Op1.getValueType(),
-                             Op1, Op2));
+  SDNodeFlags Flags;
+  Flags.setExact(isa<PossiblyExactOperator>(&I) &&
+                 cast<PossiblyExactOperator>(&I)->isExact());
+  setValue(&I, DAG.getNode(ISD::SDIV, getCurSDLoc(), Op1.getValueType(), Op1,
+                           Op2, &Flags));
 }
 
 void SelectionDAGBuilder::visitICmp(const User &I) {