[Mlir-commits] [mlir] [mlir][arith] wide integer emulation support for fpto*i ops (PR #132375)

[Jakub Kuderski]

================
@@ -974,6 +974,126 @@ struct ConvertUIToFP final : OpConversionPattern<arith::UIToFPOp> {
   }
 };
 
+//===----------------------------------------------------------------------===//
+// ConvertFPToSI
+//===----------------------------------------------------------------------===//
+
+struct ConvertFPToSI final : OpConversionPattern<arith::FPToSIOp> {
+  using OpConversionPattern::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(arith::FPToSIOp op, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    Location loc = op.getLoc();
+    // Get the input float type.
+    Value inFp = adaptor.getIn();
+    Type fpTy = inFp.getType();
+
+    Type intTy = op.getType();
+    unsigned oldBitWidth = getElementTypeOrSelf(intTy).getIntOrFloatBitWidth();
+
+    auto newTy = getTypeConverter()->convertType<VectorType>(intTy);
+    if (!newTy)
+      return rewriter.notifyMatchFailure(
+          loc, llvm::formatv("unsupported type: {0}", intTy));
+
+    // Work on the absolute value and then convert the result to signed integer.
+    // Defer absolute value to fptoui. If minSInt < fp < maxSInt, i.e.
+    // if the fp is representable in signed i2N, emits the correct result.
+    // Else, the result is UB.
+
+    TypedAttr zeroAttr = rewriter.getZeroAttr(fpTy);
+    Value zeroCst = rewriter.create<arith::ConstantOp>(loc, zeroAttr);
+
+    Value oneCst = createScalarOrSplatConstant(rewriter, loc, intTy, 1);
+    Value allOnesCst = createScalarOrSplatConstant(
+        rewriter, loc, intTy, APInt::getAllOnes(oldBitWidth));
+
+    // Get the absolute value.
+    Value isNeg = rewriter.create<arith::CmpFOp>(loc, arith::CmpFPredicate::OLT,
+                                                 inFp, zeroCst);
+    Value negInFp = rewriter.create<arith::NegFOp>(loc, inFp);
+
+    Value absVal = rewriter.create<arith::SelectOp>(loc, isNeg, negInFp, inFp);
+
+    // Defer the absolute value to fptoui.
+    Value res = rewriter.create<arith::FPToUIOp>(loc, intTy, absVal);
+
+    // Negate the value if < 0 .
+    Value bitwiseNeg = rewriter.create<arith::XOrIOp>(loc, res, allOnesCst);
----------------
kuhar wrote:

Since this is a second time for this to come up, I think we should add subi emulation and use that in both places:
https://github.com/llvm/llvm-project/blob/236f938ef65cc9028801303bb0bd914afca37836/mlir/lib/Dialect/Arith/Transforms/EmulateWideInt.cpp#L894-L903

Would you be able to land that in a separate PR and then rebase this one on top?

https://github.com/llvm/llvm-project/pull/132375