Implement constant folding for DivFOp

[jacksonfellows]

Summary

Add a constant folder for DivFOp. Analogous to existing folders for
AddFOp, SubFOp, and MulFOp. Matches the behavior of existing LLVM
constant folding (https://github.com/llvm/llvm-project/blob/999f5da6b3088fa4c0bb9d05b358d015ca74c71f/llvm/lib/IR/ConstantFold.cpp#L1432).

[jacksonfellows]

I do not have commit access (first-time contributor). Would a reviewer be able to commit this change?

mlir/include/mlir/Dialect/StandardOps/IR/Ops.td

 }
 
 //===----------------------------------------------------------------------===//
 // DivFOp
 //===----------------------------------------------------------------------===//
 
 def DivFOp : FloatArithmeticOp<"divf"> {
   let summary = "floating point division operation";
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // ExpOp
 //===----------------------------------------------------------------------===//
 
 def ExpOp : FloatUnaryOp<"exp"> {
   let summary = "base-e exponential of the specified value";

mlir/lib/Dialect/StandardOps/IR/Ops.cpp

 
 void DimOp::getCanonicalizationPatterns(OwningRewritePatternList &results,
                                         MLIRContext *context) {
   results.insert<DimOfMemRefReshape, DimOfCastOp<TensorToMemrefOp>,
                  DimOfCastOp<tensor::CastOp>>(context);
 }
 
 // ---------------------------------------------------------------------------
+// DivFOp
+// ---------------------------------------------------------------------------
+
+OpFoldResult DivFOp::fold(ArrayRef<Attribute> operands) {
+  return constFoldBinaryOp<FloatAttr>(
+      operands, [](APFloat a, APFloat b) { return a / b; });
+}
+
+// ---------------------------------------------------------------------------
 // DmaStartOp
 // ---------------------------------------------------------------------------
 
 void DmaStartOp::build(OpBuilder &builder, OperationState &result,
                        Value srcMemRef, ValueRange srcIndices, Value destMemRef,
                        ValueRange destIndices, Value numElements,
                        Value tagMemRef, ValueRange tagIndices, Value stride,
                        Value elementsPerStride) {