[mlir][Math] Add constant folder for ExpOp.

[jacquesguan]

Summary

This patch adds constant folder for ExpOp which only supports single and double precision floating-point.

[Mogball]

Can you fix the failing test?

[bondhugula]

mlir/test/Dialect/Math/canonicalize.mlir

234

These two can be CHECK-NEXT?

Nit: Instead of indenting "//", recommend indenting just "return".

[jacquesguan]

Address comment.

[jacquesguan]

In D130318#3672647, @Mogball wrote:

Can you fix the failing test?

Done.

mlir/test/Dialect/Math/canonicalize.mlir

234

Done, thanks.

mlir/include/mlir/Dialect/Math/IR/MathOps.td

let description = [{
 
     Example:
 
     ```mlir
     // Scalar natural exponential.
     %a = math.exp %b : f64
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // Exp2Op
 //===----------------------------------------------------------------------===//
 
 def Math_Exp2Op : Math_FloatUnaryOp<"exp2"> {
   let summary = "base-2 exponential of the specified value";

mlir/lib/Dialect/Math/IR/MathOps.cpp

return constFoldUnaryOpConditional<FloatAttr>(
         case 32:
           return APFloat(sqrtf(a.convertToFloat()));
         default:
           return {};
         }
       });
 }
 
+//===----------------------------------------------------------------------===//
+// ExpOp folder
+//===----------------------------------------------------------------------===//
+
+OpFoldResult math::ExpOp::fold(ArrayRef<Attribute> operands) {
+  return constFoldUnaryOpConditional<FloatAttr>(
+      operands, [](const APFloat &a) -> Optional<APFloat> {
+        switch (a.getSizeInBits(a.getSemantics())) {
+        case 64:
+          return APFloat(exp(a.convertToDouble()));
+        case 32:
+          return APFloat(expf(a.convertToFloat()));
+        default:
+          return {};
+        }
+      });
+}
+
 /// Materialize an integer or floating point constant.
 Operation *math::MathDialect::materializeConstant(OpBuilder &builder,
                                                   Attribute value, Type type,
                                                   Location loc) {
   return builder.create<arith::ConstantOp>(loc, value, type);
 }

mlir/test/Dialect/Math/canonicalize.mlir

 // CHECK-LABEL: @log_fold_vec
 // CHECK: %[[cst:.+]] = arith.constant dense<[0.000000e+00, 0.693147182, 1.09861231, 1.38629436]> : vector<4xf32
 // CHECK: return %[[cst]]
 func.func @log_fold_vec() -> (vector<4xf32>) {
   %v1 = arith.constant dense<[1.0, 2.0, 3.0, 4.0]> : vector<4xf32>
   %0 = math.log %v1 : vector<4xf32>
   return %0 : vector<4xf32>
 }
+
+// CHECK-LABEL: @exp_fold
+// CHECK-NEXT: %[[cst:.+]] = arith.constant 7.3890562 : f32
+// CHECK-NEXT:   return %[[cst]]
+func.func @exp_fold() -> f32 {
+  %c = arith.constant 2.0 : f32
+  %r = math.exp %c : f32
+  return %r : f32
+}
+
+// CHECK-LABEL: @exp_fold_vec
+// CHECK-NEXT: %[[cst:.+]] = arith.constant dense<[2.71828175, 7.3890562, 20.085537, 54.5981483]> : vector<4xf32>
+// CHECK-NEXT:   return %[[cst]]
+func.func @exp_fold_vec() -> (vector<4xf32>) {
+  %v1 = arith.constant dense<[1.0, 2.0, 3.0, 4.0]> : vector<4xf32>
+  %0 = math.exp %v1 : vector<4xf32>
+  return %0 : vector<4xf32>
+}

mlir/test/mlir-cpu-runner/math-polynomial-approx.mlir

 // Exp.
 // -------------------------------------------------------------------------- //
 func.func @exp() {
   // CHECK: 2.71828
   %0 = arith.constant 1.0 : f32
   %1 = math.exp %0 : f32
   vector.print %1 : f32
 
-  // CHECK: 0.778802, 2.117, 2.71828, 3.85742
+  // CHECK: 0.778801, 2.117, 2.71828, 3.85743
   %2 = arith.constant dense<[-0.25, 0.75, 1.0, 1.35]> : vector<4xf32>
   %3 = math.exp %2 : vector<4xf32>
   vector.print %3 : vector<4xf32>
 
   // CHECK: 1
   %zero = arith.constant 0.0 : f32
   %exp_zero = math.exp %zero : f32
   vector.print %exp_zero : f32
 
-  // CHECK: 1.17549e-38, 1.38879e-11, 7.20049e+10, inf
+  // CHECK: 2.22736e-39, 1.38879e-11, 7.20049e+10, inf
   %special_vec = arith.constant dense<[-89.0, -25.0, 25.0, 89.0]> : vector<4xf32>
   %exp_special_vec = math.exp %special_vec : vector<4xf32>
   vector.print %exp_special_vec : vector<4xf32>
 
   // CHECK: inf
   %inf = arith.constant 0x7f800000 : f32
   %exp_inf = math.exp %inf : f32
   vector.print %exp_inf : f32

 }
 
 func.func @expm1() {
   // CHECK: 1e-10
   %0 = arith.constant 1.0e-10 : f32
   %1 = math.expm1 %0 : f32
   vector.print %1 : f32
 
-  // CHECK: -0.00995016, 0.0100502, 0.648721, 6.38905
+  // CHECK: -0.00995017, 0.0100502, 0.648721, 6.38906
   %2 = arith.constant dense<[-0.01, 0.01, 0.5, 2.0]> : vector<4xf32>
   %3 = math.expm1 %2 : vector<4xf32>
   vector.print %3 : vector<4xf32>
 
   // CHECK: -0.181269, 0, 0.221403, 0.491825, 0.822119, 1.22554, 1.71828, 2.32012
   %4 = arith.constant dense<[-0.2, 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2]> : vector<8xf32>
   %5 = math.expm1 %4 : vector<8xf32>
   vector.print %5 : vector<8xf32>