fix: emit vector instead of scalar u1_zero in shl_with_overflow logic

Author: Justus2308

src/Sema.zig

@@ -15620,7 +15620,6 @@ fn zirOverflowArithmetic(
                 // If either of the arguments is undefined, IB is possible and we return an error.
                 // If lhs is zero, the result is zero and no overflow occurred.
                 // If rhs is zero, the result is lhs and no overflow occurred.
-                // Oterhwise if either of the arguments is undefined, both results are undefined.
                 const scalar_ty = lhs_ty.scalarType(zcu);
                 if (maybe_rhs_val) |rhs_val| {
                     if (maybe_lhs_val) |lhs_val| {
@@ -15661,7 +15660,7 @@ fn zirOverflowArithmetic(
                                     .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_elem, elem_idx),
                                 }
                             }
-                            if (!any_positive) break :result .{ .overflow_bit = .zero_u1, .inst = lhs };
+                            if (!any_positive) break :result .{ .overflow_bit = try pt.aggregateSplatValue(overflow_ty, .zero_u1), .inst = lhs };
                         },
                         else => unreachable,
                     }

src/Sema/arith.zig

@@ -1895,10 +1895,10 @@ fn intShlWithOverflow(
     const info = lhs_ty.intInfo(zcu);
 
     var lhs_space: Value.BigIntSpace = undefined;
-    const lhs_bigint = lhs.toBigInt(&lhs_space, zcu);
+    const lhs_bigint = try lhs.toBigIntSema(&lhs_space, pt);
 
     const shift_amt: usize = @intCast(try rhs.toUnsignedIntSema(pt));
-    if (shift_amt >= lhs_ty.intInfo(zcu).bits) {
+    if (shift_amt >= info.bits) {
         return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs, rhs_src, vec_idx);
     }
     var result_bigint = try intShlInner(sema, lhs_bigint, shift_amt);