[mlir][Sol] Fix ABI tuple decoding for narrow integer array elements

During ABI tuple decoding of array elements, values narrower
than 256 bits were written to memory without proper extension.
In this case narrow integers are placed in the high bits of
the slot, which is incorrect.

Signed-off-by: Vladimir Radosavljevic <vr@matterlabs.dev>

Author: vladimirradosavljevic

mlir/lib/Conversion/SolToStandard/EVMUtil.cpp

@@ -858,10 +858,18 @@ Value evm::Builder::genABITupleDecoding(Type ty, Value addr, bool fromMem,
                 genABITupleDecoding(arrTy.getEltType(), offsetFromSrcArr,
                                     fromMem, tupleStart, tupleEnd, loc));
           } else {
-            b.create<yul::MStoreOp>(
-                loc, iDstAddr,
+            auto elemVal =
                 genABITupleDecoding(arrTy.getEltType(), iSrcAddr, fromMem,
-                                    tupleStart, tupleEnd, loc));
+                                    tupleStart, tupleEnd, loc);
+            auto intTy = dyn_cast<IntegerType>(elemVal.getType());
+
+            // If the element type is an integer smaller than 256 bits, we need
+            // to extend it. In case we don't do that, store will place the
+            // value in the higher bits, which is incorrect.
+            if (intTy && intTy.getWidth() < 256)
+              elemVal =
+                  bExt.genIntCast(/*width=*/256, intTy.isSigned(), elemVal);
+            b.create<yul::MStoreOp>(loc, iDstAddr, elemVal);
           }
 
           Value srcStride =