[mlir][Math] Add constant folder for Log1pOp.

[jacquesguan]

Summary

This patch adds constant folder for Log1pOp which only supports single and double precision floating-point.

[bondhugula]

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

138

This requires a comment. The log1p function wouldn't be defined for any number <= -1 since 1 + x <= 0. Trying to understand why this check is just for all negative a as opposed to a <= -1?

[Mogball]

Lgtm but please address uday's comment

[jacquesguan]

Address comment.

[jacquesguan]

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

138

Done, thanks.

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

let description = [{
 
     Example:
 
     ```mlir
     // Scalar log1p operation.
     %y = math.log1p %x : f64
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // Log2Op
 //===----------------------------------------------------------------------===//
 
 def Math_Log2Op : Math_FloatUnaryOp<"log2"> {
   let summary = "base-2 logarithm of the specified value";

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

return constFoldUnaryOpConditional<FloatAttr>(
           return APFloat(log10f(a.convertToFloat()));
         default:
           return {};
         }
       });
 }
 
 //===----------------------------------------------------------------------===//
+// Log1pOp folder
+//===----------------------------------------------------------------------===//
+
+OpFoldResult math::Log1pOp::fold(ArrayRef<Attribute> operands) {
+  return constFoldUnaryOpConditional<FloatAttr>(
+      operands, [](const APFloat &a) -> Optional<APFloat> {
+        switch (a.getSizeInBits(a.getSemantics())) {
+        case 64:
+          if ((a + APFloat(1.0)).isNegative())
+            return {};
+          return APFloat(log1p(a.convertToDouble()));
+        case 32:
+          if ((a + APFloat(1.0f)).isNegative())
+            return {};
+          return APFloat(log1pf(a.convertToFloat()));
+        default:
+          return {};
+        }
+      });
+}
+
+//===----------------------------------------------------------------------===//
 // PowFOp folder
 //===----------------------------------------------------------------------===//
 
 OpFoldResult math::PowFOp::fold(ArrayRef<Attribute> operands) {
   return constFoldBinaryOpConditional<FloatAttr>(
       operands, [](const APFloat &a, const APFloat &b) -> Optional<APFloat> {
         if (a.getSizeInBits(a.getSemantics()) == 64 &&
             b.getSizeInBits(b.getSemantics()) == 64)

mlir/test/Dialect/Math/canonicalize.mlir

 // CHECK-LABEL: @log10_fold_vec
 // CHECK: %[[cst:.+]] = arith.constant dense<[0.000000e+00, 1.000000e+00, 2.000000e+00, 2.301030e+00]> : vector<4xf32>
 // CHECK: return %[[cst]]
 func.func @log10_fold_vec() -> (vector<4xf32>) {
   %v1 = arith.constant dense<[1.0, 10.0, 100.0, 200.0]> : vector<4xf32>
   %0 = math.log10 %v1 : vector<4xf32>
   return %0 : vector<4xf32>
 }
+
+// CHECK-LABEL: @log1p_fold
+// CHECK: %[[cst:.+]] = arith.constant 2.8903718 : f32
+  // CHECK: return %[[cst]]
+func.func @log1p_fold() -> f32 {
+  %c = arith.constant 17.0 : f32
+  %r = math.log1p %c : f32
+  return %r : f32
+}
+
+// CHECK-LABEL: @log1p_fold_vec
+// CHECK: %[[cst:.+]] = arith.constant dense<[1.38629436, 1.79175949, 2.07944155, 2.48490667]> : vector<4xf32>
+// CHECK: return %[[cst]]
+func.func @log1p_fold_vec() -> (vector<4xf32>) {
+  %v1 = arith.constant dense<[3.0, 5.0, 7.0, 11.0]> : vector<4xf32>
+  %0 = math.log1p %v1 : vector<4xf32>
+  return %0 : vector<4xf32>
+}