[Mlir-commits] [mlir] [mlir][math] Expand powfI operation for constant power operand. (PR #87081)

[Jakub Kuderski]

================
@@ -202,6 +202,70 @@ static LogicalResult convertCeilOp(math::CeilOp op, PatternRewriter &rewriter) {
   rewriter.replaceOp(op, ret);
   return success();
 }
+
+// Convert `math.fpowi` to a series of `arith.mulf` operations.
+// If the power is negative, we divide one by the result.
+static LogicalResult convertFPowICstOp(math::FPowIOp op,
+                                       PatternRewriter &rewriter) {
+  ImplicitLocOpBuilder b(op->getLoc(), rewriter);
+  Value base = op.getOperand(0);
+  Value power = op.getOperand(1);
+  Type baseType = base.getType();
+  Value tempBase = op.getOperand(0);
+
+  Attribute cstAttr;
+  if (!matchPattern(power, m_Constant(&cstAttr)))
+    return failure();
+
+  int64_t powerInt;
+
+  // Check for Splat or Integer Attrs.
+  if (auto splatAttr = dyn_cast<SplatElementsAttr>(cstAttr)) {
+    powerInt = splatAttr.getSplatValue<int64_t>();
+  } else if (auto iAttr = dyn_cast<IntegerAttr>(cstAttr)) {
+    powerInt = iAttr.getInt();
+  } else {
+    return failure();
+  }
+
+  bool isNegative = powerInt < 0;
+  int64_t absPower = std::abs(powerInt);
+  Value one = createFloatConst(op->getLoc(), baseType, 1.00, rewriter);
+  Value res = createFloatConst(op->getLoc(), baseType, 1.00, rewriter);
+
+  Value zero = createFloatConst(op->getLoc(), baseType, 0.00, rewriter);
+  Value negZero = createFloatConst(op->getLoc(), baseType, -0.00, rewriter);
+  Value posInfinity =
+      createFloatConst(op->getLoc(), baseType,
+                       std::numeric_limits<double_t>::infinity(), rewriter);
+  Value negInfinity =
+      createFloatConst(op->getLoc(), baseType,
+                       -std::numeric_limits<double_t>::infinity(), rewriter);
----------------
kuhar wrote:

Some float types don't have infinity, see https://github.com/llvm/llvm-project/blob/a67b9326cd0448072a1192951f12f3927f31af8c/llvm/include/llvm/ADT/APFloat.h#L151-L194 and https://github.com/llvm/llvm-project/blob/a67b9326cd0448072a1192951f12f3927f31af8c/llvm/lib/Support/APFloat.cpp#L127-L143 .

It would be safer to construct an APFloat with the correct semantics for this float type and use `APFloat::makeInf` that handles this: https://github.com/llvm/llvm-project/blob/a67b9326cd0448072a1192951f12f3927f31af8c/llvm/lib/Support/APFloat.cpp#L4475-L4485 .

We should also have a test that covers this.

https://github.com/llvm/llvm-project/pull/87081