[mlir][Math] Add constant folder for Log10Op.

[jacquesguan]

Summary

This patch adds constant folder for Log10Op which only support single and double precision floating-point.

[Mogball]

mlir/test/Dialect/Math/canonicalize.mlir

188

I'm not certain what the best practice is with regards to floating point values in lit tests. I know people have encountered precision issues with lit tests before. What have you seen elsewhere in the codebase?

[jacquesguan]

mlir/test/Dialect/Math/canonicalize.mlir

188

I use the same way with other mlir lit test cases, just like mlir/test/Dialect/Math/polynomial-approximation.mlir.

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

let description = [{
 
     Example:
 
     ```mlir
     // Scalar log10 operation.
     %y = math.log10 %x : f64
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // Log1pOp
 //===----------------------------------------------------------------------===//
 
 def Math_Log1pOp : Math_FloatUnaryOp<"log1p"> {
   let summary = "Computes the natural logarithm of one plus the given value";

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

return constFoldUnaryOpConditional<FloatAttr>(
         if (a.getSizeInBits(a.getSemantics()) == 32)
           return APFloat(log2f(a.convertToFloat()));
 
         return {};
       });
 }
 
 //===----------------------------------------------------------------------===//
+// Log10Op folder
+//===----------------------------------------------------------------------===//
+
+OpFoldResult math::Log10Op::fold(ArrayRef<Attribute> operands) {
+  return constFoldUnaryOpConditional<FloatAttr>(
+      operands, [](const APFloat &a) -> Optional<APFloat> {
+        if (a.isNegative())
+          return {};
+
+        switch (a.getSizeInBits(a.getSemantics())) {
+        case 64:
+          return APFloat(log10(a.convertToDouble()));
+        case 32:
+          return APFloat(log10f(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: @ctpop_fold
 // CHECK: %[[cst:.+]] = arith.constant 16 : i32
 // CHECK: return %[[cst]]
 func.func @ctpop_fold() -> i32 {
   %c = arith.constant 0xFF0000FF : i32
   %r = math.ctpop %c : i32
   return %r : i32
 }
+
+// CHECK-LABEL: @log10_fold
+// CHECK: %[[cst:.+]] = arith.constant 2.000000e+00 : f32
+  // CHECK: return %[[cst]]
+func.func @log10_fold() -> f32 {
+  %c = arith.constant 100.0 : f32
+  %r = math.log10 %c : f32
+  return %r : f32
+}
+
+// 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>
+}